Taller

Taller

At the junction where Broadway meets Wall Street in the financial district of lower Manhattan in New York City stands Trinity Church. One of the cities' most historic buildings, the building was finished in 1846, the third church on the site, and when it was built it's eighty-six metre tall spire was the tallest building in Manhattan. This was two hundred years after the city first sprung to life at the southern tip Manhattan island, one hundred and fifty after the first church was built on the site. The street layout of the city had long since been set, and the city was pushing north into what would soon be the Central Park area, yet the view down Broadway was clear of any buildings taller than this church. The skyline view of New York seen from the East River was one of tall masted ships docked along the waterfront. During the next fifty years Trinity church would be dwarfed by buildings so tall they would disappear into the low cloud on some days. The world record for the world's tallest building would be broken again and again in the next century, first in New York, then Chicago, then moving on to the new developing countries of the far east. So, what happened? Why did America, then the world suddenly take to the skies after centuries of low-rise living and working? Where did the arificial mountain range of Manhattan, and later many other skylines around the world, come from?

Tall buildings are as old as cities themselves, whether it be castle keeps, watch towers, church steeples, minarets of mosques, lighthouses, great statues, triumphal arches, or the great pyramids of ancient Egypt and of the Aztecs in South America. The silhouette of a city skyline made from tall buildings isn't an entirely modern idea either; several great towers still stand the small Italian hilltop town San Gimigniano, giving a taste of what the medieval town looked like when all of it's wealthy families built a sea of towers above their houses, partly for security but mostly for showing off to the neighbours. Ancient bridges still stand spanning great gorges at heights that are still impressive. The Roman Pont du Gard aqueduct crosses the Gardon river near Nimes in France at 48 metres; the Puente Nuevo, north of Malaga in Spain, is 120 metres above the rocks at the bottom of the chasm the 18th century bridge spans. There has always been great symbolic importance in building tall. The higher the spires and vaults of Medieval Cathedrals climbed the closer they got to heaven. The height of a castle keep was designed to both defend and impress.

Watch towers and defensive towers obviously use the natural advantage of being up high, while the height of bell towers and minarets allow them to broadcast over larger areas. Some functions may have been lost in time; the great Pyramids of Egypt are a constant topic for debate over whether they are purely symbolic monuments or if their height and construction may have served another purpose. What is known is that the 146 metre tall Great Pyramid of Giza was the tallest structure in the world for around three thousand, eight hundred years, a time span stretching all the way from 2500 BC to 1311, when the spire of the central tower of Lincoln Cathedral outreached them by fourteen metres. The wooden spires of the building's three rectangular towers are no longer there, in case the curious visitor on seeing Lincoln Cathedral in person smells a rat in the historical record. The record breaking central spire blew down in the 16th century and was never replaced, and only one other cathedral has ever gone higher; the Ulm Minster in Germany, completed in 1890.

All these buildings were constructed from stone, brick and wood. They often stretched the limits of what was possible. Beauvais Cathedral in Northern France has the highest apse of any gothic cathedral (48 metres). From the inside it looks heavenly, from the back it looks mighty, from the front it looks conspicuously unfinished. Beauvais' cathedral's lofty nave collapsed in 1284 while it was barely finished. They put it up again with a stronger vault. Three hundred years later a 153 metre central tower fell down too. Trying to reach for the stars meant the rest of the building never came close to being finished and it stayed in it's 16th century state ever since. England nearly had it's own grand folly to match Beauvais but unfortunately for William Beckford the tower he built as the centrepiece of his home, Fonthill Abbey, fell down no less than three times. Beckford got his first two towers up to ninety metres before they both fell down. His third and last tower was a little shorter but now made of seemingly impregnable stone, concrete and plaster. Contemporary artworks show that tt looked impressive from the outside, but not that it was hopelessly unfit for purpose, it only went up so fast compared to the great cathedrals because it was far too thin and flimsy to support such heights. Much like the unfortunate Beckford himself, a stinking rich but unstable man, who hid away in his great Abbey and rarely entertained guests - a fortunate thing given the huge wobbly tower wasn't anchored in the ground but sat precariously on arches in the middle of his home (so as not to block the view down the aisle). It fell down in 1825, shortly after it's owner had sold it, now little remains except a strange half forgotten memory of Britains's strangest stately home.

Other enterprising Britons were more successful with their projects than Beckford , and left a more sensible legacy to the world of engineering. In 1779 in a small Shropshire gorge, in the middle of England, ironworker Abraham Darby the 3nd, built a arched bridge of wrought iron. The area was a hotbed of industrial activity at the time after Darby's grandfather had created a technique of smelting iron with coke (coal baked and dried in kilns), rather than charcoal, meaning coal mining could replace the need to fell trees to make iron. The "Iron Bridge" as it inevitably became known was the forerunner of every large metal frame structure in the world. Coal fuelled mass iron production revolutionised the world; molten iron ingots could be rolled into long, thin beams, that when bolted together into frames would hold up heavy loads, and span greater distances than stone arches. Bridges provided the first alternative to the ancient materials, and the first public sign that the world was soon heading into a totally different age of construction. The iron arch bridge begat the suspension bridge and astonishing new wonders of 19th century industrial Britain, like Thomas Telfords's Menai Straights bridge in Wales and Brunel's Clifton Suspension Bridge in Bristol. The great Victorian suspension bridges looked fantastic and suitably full of hubris, but there was method all the showiness, for a suspension bridge used less material than a metal truss arch bridge to span the same distances.

By the latter stages of the 19th century, iron was being supplanted by steel in bridges. Steel is iron mixed with carbon, is much stronger and more malleable than iron, and when the difficulties of making consistently good quality steel had been ironed out it took bridges to the even grander scale; the 1890 Forth Railway bridge crossed the entire Firth of Forth in Scotland and the 1883 Brooklyn Bridge connected Manhattan island east to the borough of Brooklyn across the East river. The Bridge's bridge decks and cables were made from steel anchored to stone towers, and loomed over the riverside docks, dwarfing the great sailing ships, and nearly matching the spire of Trinity church. Ironically the greatest building wonder of the 19th century; the Eiffel Tower in Paris was made from iron, not steel, so while it showed that immense heights were possible, it also did so with an obsolete building material that had a major problem. Iron was tough but it was brittle. The collapse of some iron structures had shown that it was deceptively easy to build big in iron, but harder to keep it standing when subjected to outside forces. In 1845 a disaster happened in the English city of Great Yarmouth when an iron suspension bridge over the river fell under the weight of spectators watching a circus act. Thirty four years later came the most infamous bridge disaster in the country when the railway bridge over the Firth of Tay in Scotland fell in a storm, taking a train of passengers with it. Most of the 2.7 mile bridge was a conventional iron truss bridge on stone piers but the central section had been raised to allow ships sailing down the estuary through, and that section was simply blown over by the storm.

The Eiffel Tower could have been written off in many minds as a one-off, a modern day Great Pyramid, and many did. It wasn't even meant to be permanent, it  was a centrepiece for the 1889 World's Fair, scheduled for removal along with the rest of the attractions when the lease was up. But, of course, it became far too popular for that, and with good reason. At three hundred and twenty four metres it was twice the height of Cologne Cathedral - the existing record holder. This too in age before aeroplanes, an age where nobody but a few intrepid balloonists had ever seen the like of such a bird's eye view of a city before. Steel frames worked well for bridges, and naturally piqued the interest of architects and engineers wondering how they might be used for buildings, though those innovators would not emerge from Europe but America. Several quirks of history led to New York City and it's counterpart seven hundred miles west, Chicago to became the early hotbeds of tall buildings. Both sat a the sites of important harbours; New York at the meeting of the Hudson River and the Atlantic Ocean, and Chicago at the base of Lake Michigan, where the eastern United States met the wild west. Both suffered fires that cleared out much of their old buildings; the Chicago fire of 1871 was most disastrous, wiping out the old wooden city.

Both were flat, with strong bedrock under the surface. But the presence of water meant both also had limited space in the middle as more and more people moved from the countryside, and the "Old World" over the ocean, to the industrialising American cities in the 19th century. The influx of people drove up crowding, and land prices. These latter factors set the gears rolling with urban planners, engineers, money men and all the rest - after all land prices didn't include the space above the ground. The industrial revolution, and all it had brought had created whole new types of city buildings; giant mills and factories, urban offices, and people now living in multi-level tenements. The more floors that could be piled on, the more people, machines, and offices could be crammed in. The opening of the Erie canal connecting the Hudson river with the great lakes across upstate New York, really set the economy of Manhattan on a roll that hasn't let up. The Canal brought easy trade across half of the country; cargo could leave Chicago, cross the lakes, come down the canal to New York, and then on to the world. Being at the crossroads of so much trade and immigration, the tip of Manhattan quickly became one of the most important, rich, and densely populated places in the world. Followed, not far behind in the ranking by Chicago, San Francisco, Philidelphia, and many other emerging American cities.

The first signs of what was to come emerged in Chicago... or New York, depending on who one asks, or how the various definitions of what would come to called a "skyscraper" are made. There were early murmurs in the mid-19th century in New York - the six storey Holt's Hotel is sometimes considered the first ever high rise building in the city. It was conventional in construction, as was the Equitable Life Assurance building, a seven storey office put up in 1870 on Broadway. In spirit this building was the first high rise office in New York City, and would probably have been joined by many more in 1870s had financial crisis not taken over in the middle of the decade and temporarily slowed developments. The first steel framed office building is generally agreed to be the Home Insurance Building in Chicago. Built in 1885, it towered to the giddy heights of ten storeys. It's engineer William le Baron Jenney had been a classmate of the great French tower engineer Gustave Eiffel in Paris, and clearly had been inspired to follow a similar path, though his creation predated the Eiffel Tower by four years. This building had a partial steel frame, and still included some iron sections, and some of the masonry carried weight, so there is contention to whether it truly counts as the grandparent of all the future skyscrapers. It's main role was to convince the many doubters that such a technique was viable.

Not everyone was convinced that a metal frame faced with masonry to keep out the weather was a good idea. Much like with the Trinity Church in New York, the Chicago Water Tower of 1869 was the tallest building downtown, and few people could imagine a world where it would be dwarfed on all sides by buildings with new fangled metal skeletons. Ironically the Home Insurance company who paid for it was the "New York" Home Insurance Company, and they took the title of Birthplace of the Skyscraper away from their home city and gave it to Chicago. Four years passed, the Home Insurance Building was a complete success - it stood up, had more useable space, and used less material than it's masonry neighbours, and copycats quickly sprung up in the centre of Chicago, among them the first full steel frame building in the world; the ten storey headquarters of the Rand McNally publishing company. By contrast the hulking all-masonry Monadnock Building had walls two metres thick at street level, and sunk half a metre into the ground over the subsequent decades, despite it's cutting edge steel and concrete foundation. Later in the same year New York would catch up with the all steel, eleven storey Tower Building. The city fathers in the city had been even less keen than many had been in Chicago and hadn't permitted steel frame buildings until 1889, when the Tower Building's designer Bradford Gilbert, persuaded them to relent. To much skepticism he'd argued that the tower was effectively a truss bridge standing on it's end, and his point was proven when a heavy storm failed to knock it over later in the year. The tide quickly turned and New York soon caught up, and passed Chicago, both in terms of number and height of it's skyscrapers, a position it would hold for another eighty years, when Chicago's Sears Tower would dethrone New York's World Trade Center as the tallest American building.

There were a couple of interlopers in the race to be the world's tallest building. Clearly the Eiffel Tower was the tallest structure, though since it was only an observation platform (and later a radio mast) it wasn't truly counted as an occupied building. Some of the great European cathedrals still peaked higher; Rouen, Cologne and Ulm all had spires over 150 metres high. The construction of a vertiginous City Hall in Milwaukee in 1895, gave the small midwestern brewery town the title of tallest office building for a few years, followed by the Philadelphia City Hall in 1901. That building is still the tallest pure masonry building in the world, taller than any cathedral. But despite these flourishes Manhattan was still the place where the most new skyscrapers were rising.  One of the city's newspapers had put up their own masonry office block in the 1870s, the nine storey Tribune Building. To put one over on their rival paper, the New York World built their headquarters practically next door, only they made it twenty stories, and in doing so passed the height of the Trinity Church spire. To add to air of dominance the new king of the city had a great golden dome, where it's owner - Joseph Pulitzer of Pulitzer Prize fame - had his office. Not to be outdone by newspapers, the insurance companies caught up again in 1894 with the Manhattan Life Insurance Building, passing over one hundred metres, a first for any office building.

Many of these pioneering skyscrapers have been demolished, all in their way a victim of their own success, replaced by bigger and better buildings on land valued much more highly than before. The Equitable Building was gutted by fire and then replaced by a larger successor, the Tower Building came down in 1914, the Home Insurance Building in 1931, the Rand McNally in 1911, the Tribune in 1966, the Manhattan Life Insurance in 1963, the World Building in 1955 - to make way for more lanes of traffic onto the Brooklyn Bridge. Le Baron Jenney's 1889 Manhattan Building, (all but inevitably given the name it stands in Chicago), claims the title of oldest metal frame skyscraper still standing, though the half frame, half masonry Chicago Rookery Building is older still. Oddly the heavy brick Monadnock Building is still there too in central Chicago, it's colossal street level walls still housing tenants. It is still the tallest brick building in the world, a sign of how quickly the new way to build took off. The Wainwright Building, built in 1891 in St Louis, designed by Louis Sullivan the tutor of Frank Lloyd Wright, also still stands, the most prominent early high rise outside of Chicago or New York and an early example of the minimalist function-over-form style that would become standard in the next century - so much so that it is often called the first ever modernist building.

A rare survivor in New York is the 1899 Park Row building. At the time it's twin cupolas gave it the original "Twin Towers" moniker of New York, the building was the tallest in New York for nearly a decade until being topped by the nearby Singer building. The Singer, home base for the sewing machine company, took the title of tallest building away from the Philadelphia City Hall, and stood at the top of the tree for one year until a building further up town took the title away. By this time the land around Broadway and Wall Street, the administrative centre of New York for two centuries, had become the most expensive in the world, and some builders were looking uptown for new, more open, pastures. In 1903 the iconic Flatiron building rose at the intersection of Broadway, 5th Avenue, and 23rd street, two miles uptown from the financial centre. The diagonal Broadway crossed the grid pattern giving the Flatiron - engineered by Chicago based engineers - a unique triangular plot. Though it never competed for any height records, it's dramatic location meant the building is easily the most famous of American "Gilded Age" skyscrapers. It also became famous at the time for the "Wind tunnel" effect it created at the junction blowing up the skirts of passing women, thus allowing the gentlemen of the 1900s a tantalising dash of ladies ankles.

Nearby, a block away across Madison Square Park, the next generation of New York's skyline went up in 1909. The Metropolitan Life Insurance Tower pushed the new mark above two hundred metres, looking down on the Singer Building by a clear seventeen metres. Downtown didn't wait too long to reply; opposite City Hall the retail magnate Frank Woolworth was putting up his eponymous corporate headquarters. The Woolworth Building, or the "Cathedral of Commerce" as it became known, took three years to go from commission to opening day, cost thirteen million dollars, and stood two hundred and forty one metres from street to pinnacle. The fat cats of lower Manhattan were back on top, albeit with the help of the creator of a dime store chain and it's customers; F. W. Woolworth hadn't enlisted any other investors except for a bank, and he bought their shares out soon after the building was finished, so the great skyscraper was, more or less, paid for by the public's cash. Many of the same public would go to work in the building, as the company that built it only needed a fraction of the space inside, so many other businesses flocked to occupy it's floors. The so called "white collar" office had changed a great deal in the new age of the skyscraper, and filled up the new spaces with all kinds of stuff. There were telephones, typewriters, rooms full of paperwork, electrical generators, water pumps, boilers, and - most astonishing for many observers - was the sight of a not inconsiderable number of women, working as clerks and typists. The modern world was on it's way.

The Woolworth Building stood proud as the world's tallest skyscraper for seventeen years. The Great War came and went, a dramatic new law prohibiting the sale and consumption of alcohol arrived, gangsters became household names, jazz music and 'flappers' dancing suggestive new dances became the new crazes, the American economy boomed and New York City opened a new train terminal. The Grand Central Terminal brought masses of people onto 42nd street in midtown Manhattan, many of them heading for the Jazz clubs, theatres and other hangouts around Broadway, and increased investment in the area. Newspapers were among the first to embrace the "Roaring Twenties" to start deserting the old downtown for the newly fashionable end of town. Times' Square was originally called Longacre Square until the New York Times moved in in 1904. A similar boomtime was happening in Chicago, an elevated railway was built at the turn of century in a loop around the downtown - the box like shape of the the area giving it's colloquial nickname "The loop" - and lifting bridges were stretching across the river. On the north side of the river front two of Chicago's most beloved skyscrapers, the Wrigley Building, and the Tribune Tower, went up opposite each other, giving a city panorama that rivalled that of the city hall park in New York. The 1920s saw other American cities muscling in on the action; Cleveland, Los Angeles, Detroit and Houston all built their own landmark tall towers, though nowhere near the level of Manhattan.

Nothing topped the Woolworth Building though, until in 1929 two rival projects began to rise over Wall Street and 42nd street respectively. In one corner stood the might of the Bank of Manhattan, in the other the Chrysler automotive colossus. The two rival architects, Harold Craig Severance and William van Alen, faced off with a dash of personal rivalry thrown into the mix as the two had been business partners for thirteen productive years until their respective egos could no longer tolerate the other. The former looked like he would win the battle; when his Bank of Manhattan building at 40 Wall Street was topped out with a great copper-coated pyramid cap in April 1930 it stood a record breaking 283 metres tall. Unbeknown to Severance and his clients, across town at the Chrysler Building his former partner had a secret plan to snatch the title. A forty metre tall decorative spire was built inside the tower and hoisted into place a month after the Bank of Manhattan Building was finished, bringing the Chrysler Building up to 319 metres and taking it past the Eiffel Tower's height too for good measure. The gaudy pinnacle was the tallest thing ever built, no matter how it was measured. The opposition, understandably a little deflated, tried to publicise the undeniable fact that the Bank of Manhattan Building actually had a higher top floor than it's rival. But the contest was already being overshadowed by two other events. The first was the great stock market crash of October 1929, when shares on the New York Stock Exchange lost thirty billion dollars in value in two days, which by mid 1930 was showing signs of leading the American economy into a major downturn. Eventually the Great Depression would kill off, or downsize many skyscraper projects, and bring the golden age of the late 1920s to a crashing halt. The other thing was literally putting the Chrysler Building in the shadow; the Empire State Building.

This actually wasn't quite true; In summer 1930 the foundations of the Empire State Building were being constructed half a mile from the Chrysler, and the finished building wasn't planned to be quite that tall. It would still be a mighty edifice though, and it would go up mightily quickly. All 381 metres and one hundred and two floors would be lifted into place in just over a year. It wasn't just the height either that impressed; the building had twice the volume of the Chrysler Building. Not that the extra space would be needed for many years. The Depression was already biting on Manhattan and the space inside was not even half full throughout the 1930s. The "8th Wonder of World" was one nickname bestowed; the "Empty State Building" was another. Even as the country, and then the world, reeled from the sudden austerity and hardship brought by the economic crash, few might have guessed that the Empire State Building, extended to 443 metres with a new radio mast on the top, would be the tallest office building in the world for the next forty two years. The long stay as tallest building was telling. It showed that it was a very impressive achievement but not one others were keen to emulate, no matter how iconic it was. Twenty years passed, and another World War was fought, before the Empire State Building turned a profit from hiring out to tenants.

The post war world was a time of great prosperity in American cities, though this did not equate to any height records being broken. The new United Nations building on the East River shore in Manhattan set the tone. Like its occupant organisation it was a brave new idea; the glass curtain wall building, the same steel frame but coated in shiny reflective walls of glass rather than terra cotta masonry. The walls and windows had become one but improvement in glass technology wasn't the only driver in bringing in the glass box look. Glass walls had been around for surprisingly long time, the first being the small Oriel Chambers building in Liverpool built in 1864 but not received at the time with much enthusiasm. So in theory making glass walls was possible, but in reality too complicated and expensive to be worth the effort. Glass sheets are relatively easy to make for houses and cars, But, as anyone who has accidentally smashed window glass can attest, it is brittle stuff, and anyone who has been woken up by a gale will also relate, regular glass won't stand up to much punishment from the elements.

Like many other materials it is the structure and flaws in it that make Glass brittle. Find a way to form molten glass without creating flaws and glass can be made much stronger.  The first manufactured glass was made by blowing it out in molten state as if to make a jug, then spinning out the disc into a large circular pane, (hence the small wobbly looking windows of medieval and Tudor English buildings). Glass and steel have a connection that stretches back to the 19th century as Henry Bessemer the British engineer who perfected the process for mass producing steel also pioneered an industrial production method to make rolled sheet glass. Bessemer's glass wasn't perfect and a better option for higher quality was to cast glass on a flat surface; ideally molten tin was the best material, as it was easily available, stable and denser than glass, the hard part was making it economical to make in factories. In the 1950's the Pilkington company in Britain developed a cost effective tin casting method, making them into an industrial giant, and sending the glass wall style skyscraper to all corners of every corner of every city centre in the world, as affordable high strength glass was now in every engineers recipe book.

Electric lighting and telephones had made the first generation of skyscrapers useable, but it took many years of improvements in technology to make them more economical. The creation and of air conditioning was a crucial step to bring along the next generation as without cooling the glass windows would create a greenhouse in the summer. The older skyscrapers were often surprisingly poky inside and every effort was made to get near a window. By the 1950s the problem was lessened by the fluorescent light strip, another wonder invention that meant office workers didn't need to stick their desk by the window to see, and designers could make much larger floor spaces and owners could command more rent money. Skyscrapers could move on from being the vanity projects of the wealthy few to properly paying their own way. There was another change by the 1950s; cars. The workers of the 1920s came to work by subway train or streetcar, even the managers (in the 1900s John D Rockefeller rode the elevated railway to get from his upper east side mansion to his office, despite the occasional verbal potshot from other passengers). But by the jet age private cars were everywhere and skyscrapers needed big underground car parks. A new style grew up that dominated for the next twenty years; big pedestrian plazas and glass walled towers standing behind. Banks and corporations were more interested in taking over the world, with their shiny glass headquarters, nobody seemed interested in going for height records. Only with the advent of the World Trade Center proposal in the 1960s did the Empire State Building's record look under threat again.

At the time the WTC was the largest application of a whole new design theory, one that dragged the past into the present, and overturned eighty years of practice. Since the first steel framed office buildings the outside walls had been there to keep the weather out and for decoration. The entire structure was the heavy steel frame underneath - in other words a 1920s skyscraper could stand up without any of the outer walls if they were removed. Or, perhaps, one could turn the skeletal Eiffel Tower into such a structure with some masonry and windows. With advances in materials in the 1950s and 1960s engineers considered a new approach, one with several big advantages. Instead of a uniform framework a tower could have a central core with lightweight floors attached to it and held up on the outer edge by the outside walls. The solid centre is rigid and strong, and contains the stairs, lift shafts, pipes and cables, while the floors and outer walls can be dynamic and flex - all while saving massively on weight and materials compared to the previous designs.

The so-called tube frame design might seem obvious and simple - but on such a scale it could only come about thanks to stronger, lighter, steel and concrete. At it's opening the large, open plan floors of the Trade Center towers were their big selling point. There were no columns in the way of the floors, and every floor had the same layout. True, because the vertical outside wall columns were so tightly grouped together the windows in the outer skin were thin slivers, but, as the architects pointed out, this was not necessarily a bad thing for those inside looking out from such heights. The building's design also meant that many of the vital parts were duplicated over and over again on each floor, and all could be prefabricated and hoisted into place like a giant children's construction kit. The 417 metre North Tower of the World Trade Center overtook the Empire State Building as the world's tallest building in 1970, followed a little later by it's slightly shorter twin (the South Tower's structure was identical but it did not have a large communication mast like the North). Not everyone was convinced by the two giant silver steel boxes lording it over the southern end of Manhattan. In one of the greatest 20th century cultural put-downs they were described as looking like the "boxes the Chrysler and Empire State Buildings were delivered in".

Taking the Empire State's crown didn't help endear The World Trade Center to many people either, though it didn't hold it's title of World's Tallest for long. After decades playing second fiddle Chicago really was going to steal New York's thunder in the 1970s. In fact, by the end of the 1960s the windy City was already showing it's hand, after two decades of inactivity. The tubular skyscaper concept had been pioneered by Chicago-based engineer Fazlur Khan in the mid-1960s, and in 1969 his John Hancock Center rose over the North end of the city, a few blocks north of the Wrigley and Tribune Buildings. The Hancock was not the tallest building in the world, but it was the most dramatic looking. The tube system in this building was built around giant triangular braces on the side the frame, and the sides tapered in. In a world that was used to sober rectangular boxes, the giant trapezoid tower showed that the future was going to be big. Quite how big was shown four years later when the 442 metre tall Sears Tower was completed in the middle of the Chicago loop. The Sears Tower was really the Sears Towers, as it was a grid of nine of braced tube frame boxes all bunched together, extruding upwards to different heights, with the two in the middle making the top of the tower. The architects finished this tower in black, to match it's companion across town. Forty years after the Empire State and Chrysler Buildings had formed the perfect highrise double act in the New York, history had repeated itself in Chicago.

By 1972 there was even a World Trade Center copy in Chicago too; the Aon Center looked almost identical, except it had no twin standing alongside. Chicago's own "Twin Towers" were the Marina City residential towers. A pair of concrete cylinders on the edge of the Chicago river facing downtown, the first nineteen floors were open sided car parks, as if the cars were afforded nearly at the same status as their owners, the residential floors have the same structure as the car parks but with glazing and balconies. Marina City looked like the future of cities, and given that the building has aged well and weathered  better than many concrete structures, it still does. Chicago birthed some of the first residential tower block complexes, and many of the originals are still some of the best, particularly the three black buttresses of the Lakeview Tower, one of the cities most distinctive landmarks, standing like a lighthouse on it's own promontory sticking out into Lake Michigan.

The Sears Tower stood as the tallest building in the world until 1997, showing just how quickly the tubular skyscraper reached the limit of what was economically feasible. To go any taller the Sears Tower would have had to take up far more ground space than the one block of Chicago than it did. What happened instead of record breaking was an explosion in styling and creativity; the 1980s became the era of postmodernism, when the skyscraper became advanced enough to start morphing into different shapes and styles. Retro came back with designers mimicking some if the styles that went before. It also went international. The sears was the last American skyscraper to hold the title of tallest. It was replaced at the top by the twin Petronas towers in Kuala Lumpur Malaysia - the kind of far eastern emerging capital city that became the new hotbed of the 'supertall' as the new name being used more and more to distinguish the new breed of buildings standing well over four hundred metres tall became known. The forerunner of all this eastern promise is undoubtedly Hong Kong. the former British protectorate of China has long been the Manhattan of Asia even if it has never held the tallest skyscraper title. It has the same circumstances of lack of space and proximity to water that drive skyscraper booms. When it was returned to Chinese rule in 1997 it was easily the most glitzy city in Asia with no contenders. That would change. The structural spires on top of the Petronas towers took them past the Sears Tower, not their floor count, leading to great debate trying to clarify exactly what should count as part of the building's height.

These arguments were stopped dead by the events of September 11th 2001. The targeting of the World Trade Center towers sent major ripples through the world of architects, engineers and city planners. The worry was that in the new information age, where people could work from just about anywhere, would anyone be all that interested in being up high in offices anymore, especially given that they were obvious targets for major attacks. The worry faded away during the next few years, overtaken by larger concerns about the world economy and the American financial crisis of 2008 creating fears of a new great depression and worldwide economic disaster. In 2004 the Petronas's record gave way to Taipei 101 in the heart of the Taiwanese capital, a building planned and started before 9/11. But still, despite the unforgettable sight of the towers in New York crumbling down, the new skyscrapers kept coming: In Shanghai the 420 metre Jin Mao tower from 1999 was joined by the even taller Shanghai World Financial Center in 2008. At nearly five hundred metres, even this is now in the shadow of the 632 metre Shanghai Tower, finished in 2015. All three stand adjacent to each other, the closest conglomeration of such 'supertalls' in the world. The metropolis of Shanghai is a 'new' New York if ever there was one, though the United Arab Emirates might dispute that conclusion. The UAE has been oil rich for decades but only in the 2000s did tall towers start emerging from the desert on the shore of the Persian Gulf. Taipei 101 ceded the 'Burj Khalifa' tower.

The 828 metre tall tower suffered through the same problem as the "Empty" Empire State. The world economy was picking itself up from the seismic shocks of the late 2000s, and customers for space in the new wonder tower were hardly queuing from the Dubai airport arrivals. The "Ground Zero" World Trade Center site took many years to grow again, and for ten years the seventy year old Empire State Building was again the tallest skyscraper in New York. Perhaps even more bizarre was the fact that the long-overlooked, and slightly run down 1930s skyscraper called 70 Pine Street was again the tallest building in the Financial district. The new One World Trade Center tower, replacing the lost twin towers, was finished in 2014 and retook the title of tallest building in New York, and indeed the USA, though the latter title is a disputed technicality. The newcomer's roof is actually lower than the top of the Sears Tower (now under new ownership and renamed the Willis Tower) but the decorative spire on the former is counted as part of the structure where the twin antennae on the latter are not.

The tall building trade's latest trend is now the supertall residential tower. Most of the new skyscrapers of the 2000s have been multi-use, there being so much space inside that offices share the building with hotels, apartments, casinos etc. There had been multi use before; the John Hancock Centre in Chicago was a pioneer when it opened with residential and office space, but towers consisting only of apartments have come more and more into vogue as costs have come down. The Empire State Building is now the third tallest on the New York skyline behind the new 1 World Trade Center and 432 Park Avenue, a daringly thin design with a square cross section that resembles nothing as much as a stack of Lego bricks. At 92 million dollars the 95th floor apartment at the top is the most expensive view in the world. Naturally such in-your-face displays of wealth conjure up plenty of indignant reaction from the mere drudges living in the the shadow of the the infamous 1 percent-ers, literally looking down their noses at the hoi polloi, if they are home at all and not just using the property as a place to rest their money. As the writer Simon Jenkins puts it in a column the
new buildings form; “an eccentric economic microclimate or tax-evading savings parked in the sky” Though in their defense the newcomers can encourage and international clientele; Manhattan is old and moneyed and notorious for its residential boards, who hold all the cards, and will vet anyone who want's to live in their apartment buildings. So when a supertall comes along and throws it's doors open to anyone with a thick enough wad of money the appeal to outsiders is clear.

Burj Khalifa shows how far technology has come in a century, both in terms of the height it reaches and the relative ease of its construction. It took years to plan and put up, but no major upsets affected it. Essentially the only reason it has stood unchallenged is so far only one developer has been willing to put up the money to pay for it, and the UAE has accommodating planning rules, plenty of open, flat, space, and - whether anyone cares to admit or not - plenty of cheap labour from across Asia.
Doubtless there are developers who would love to plonk something similar down in Manhattan or London, or Hong Kong, but there would be many complications. The Burj Khalifa stands alone its own large area surrounded by landscaping; trees and water features and the enormous mall of Dubai.
Take the same area and place it on new York and it covers most of lower Manhattan's financial district. Then there's the matter of aesthetics; a few extra high rises in London's financial district have caused a decade of debate among locals and media commentators alike. As Will Self has it about London's new look centre; "The detailing is so profuse and so gimmicky that the viewer resists being ensnared by balustrades and caught up in arrases of pampas grass, her eye flees from one behemoth cartoon outline to the next, before giving up and simply goggling at the whole winking, steaming, lit-up panoply". The conclusion both defends the excitement of the sight, and criticises the shallowness of it.  Some critics are more blunt; The Verizon Building, 160 metre telephone exchange built in 1975 at the foot of the Brooklyn Bridge "overwhelms the (bridge) towers, thrusts a residential neighborhood into shadow and sets a tone of utter banality." (the verdict of the New York Times architecture critic.) Stephen Bayley calls the Burj Khalifa "vast in size but small in meaning" and a
"frightening, purposeless monument to the subprime era". If scale and symbolism have always been controversial, then the rights given to those who do the dirty work and actually put them up has been an equal quagmire of opinions. Finding people who will build giant skyscrapers but don't demand the entire budget in wages is less straightforward in North America and Europe than perhaps it is in the Middle East. As is the amount of bureaucracy and paperwork involved. This has not gone unnoticed.

But of course the great Western metropolis have had a century head start to grow into their iconic shapes, for better of for worse. The east in the 2000s is following the same process that the west went through in the 1920s and 1930s. Grand schemes made possible by low wages and unpleasant work conditions was a regular occurrence in the west, until fairly recent times. The famous 1931 Charles Ebbets photo of the construction workers having lunch sat precariously on the girder of the Rockefeller Center, makes things look like a jolly jape, but it was still tough, very dangerous work. The men in the photos undoubtedly posed for the occasional goofy snapsnot with a keen sense of how precarious their job was. Five men died during the two years the Empire State building went up. The same number died decades later constructing the Sears Tower, including three in one incident. Twenty seven had been lost to the Brooklyn Bridge, eleven to the Golden Gate. All this  paled to the Hoover Dam in Nevada; that racked up a body count close to one hundred. The seeming wonderland of Dubai has a few problems under the shiny surface; the sewage system under the ground lagged behind the construction above it during the 2000s, requiring a fleet of tankers to haul it away from some areas. Whether the skyscraper boom in Dubai will last, or if it will go the same way as the 1930s boom in America and twenty fallow years will pass remains to be seen.

Burj Khalifa Also follows another western pattern: the tower tops out at 829 metres but it's observation deck is 555 metres and it's top useable floor is 584 metres. In other words the tower has a 244 metre mostly decorative spire. Or when standing on the observation deck there is two thirds of an Eiffel Tower's worth of unoccupied tower above. In fact, the shorter Shanghai tower, officially the world's second tallest, has the higher visitor level. The "supertall" boom of the 2000s isn't quite as tall as it looks on first impression. The flat roof of the Sears Tower is not much lower down the horizon than the working guts of the Burj Khalifa. In another echo of history repeating, just like the Chrysler Building it was not originally intended to be nearly so tall, but 'in for a penny in for a pound' seems to apply to skyscraper designers and the lure of new records was hard to resist. Given the iconic status the Burj has already attained it might spoil the illusion a little to know that it was being put up before it's design was finalised, so as to save money, and the building was planned to be entirely residential, but plans again changed on the fly and it became multi-use. Not that this takes away from the achievement of the designers and builders. The tubular construction manages to be technically capable without being a purely functional lump of concrete.

Concrete may not be glamorous, but it is still a highly advanced technology that has evolved throughout the skyscraper age, an ancient Roman invention now being pumped up hundreds of metres above the trucks delivering it. The renaissance in concrete construction started in the 1950s with the start of a new branch of the tall building tree. The development of reinforced lighter concrete coincided with the post war rise in television and radio, the natural conclusion being the creation of concrete TV masts for broadcasting the signals far and wide. It was a whole new type of tall building, although the designation has always been contentious. Tall 'buildings' it is usually said, are supposed to be occupied all the way up and continually occupied. Anything else doesn't count, so spires and towers, while reaching impressive heights, don't really compare to skyscrapers. The creation of concrete TV towers in the 1950s blurred this boundary somewhat. The Stuttgart Fernsehturm (the best German translation of 'television tower'), built in 1956, set the template. The five storey pod three quarters of the way up contained observation decks, television broadcasting equipment, a cinema, and that feature that would become synonymous with space age design and the 1960s, the revolving restaurant.

The obvious publicity benefit of having a tall lookout spot on top of the television broadcasting mast inspired a good number of imitators. In Germany alone there were TV towers built throughout the country, the largest of all protruding from East Berlin. Built in 1965 as a public demonstration of the the might of the DDR, looking down on the American and British sectors of the divided city, the Berlin Ferhnsehturm endures where the Berin Wall and the East German parliament building have long since been razed, the concrete and steel stiletto turned from Communist ornament to popular tourist attraction and nightspot. Tallest of all was the Ostaniko Tower in Moscow, completed in 1967, the Ostaniko took the tile of tallest 'Freestanding structure' (rather than building) from the Empire State Building. Though it had a had a hint of the R7 Soyuz rocket booster in it's space age shape, hidden behind the Iron Curtain, where few outsiders could see it, it was a footnote compared to the Soviet space missions. For decades the king of the TV towers was the Canadian National, or CN, Tower in Toronto. Built between 1973 and 1976 it stands 553 metres; holding the world record for tallest structure for thirty four years until the Burj Khalifa passed it. Oddly it was built not by a TV company but the Canadian rail company, and ironically it's height was necessary to get the CN tower's broadcast signals  past the city's other tall buildings. Had it been plonked in the middle of Manhattan the CN Tower would have been impressive, but crowded for attention. On the shore of Lake Ontario, it had the skyline of one of the continent's largest cities to itself.

Architects and engineers may design a skyscraper but it is the construction contractors who have to put the thing up. The problem with a very tall building is that two of the most useful building tools for erecting low rise buildings - scaffolding and the tower crane - are not much good at higher levels. Tower cranes can only go so high before they cannot reach and no one in their right mind would try to building scaffolding up to heights of hundred of metres. The builders main challenge is working out how to keep a construction standing when it's not finished. On lower buildings made from masonry they can put up bracing to hold things up, a technique that stretches back to ancient times. This was another big advantage of steel frame construction in the late 19th.century; once each floor of a solid steel frame skyscraper was finished it could be the staging post for the next one - no scaffolding required. The workers could take temporary lifts and ladders up the framework and add pieces on. This led to some of the most famous images of 20th century city life in the 1920s and 30s as the steelworkers stood on open girders like acrobats with the whole of New York or Chicago below them.

While the frame was going up the lower floors could be finished off by the armies of electricians, plumbers and all the rest. This partly explains why towers like the Empire State could be finished with such speed. The next step in improving efficiency was the stick the crane on the rising structure too.The so called "kangaroo" crane, so named because of its function and Australian origins sits on top of the building that it is constructing and uses hydraulics to lift itself up as the work rises below. The two Golden Gate Bridge towers in San Francisco were built by such a method in the 1930s and showed the world that big metal structures could be built successfully by cranes perched on the top. On some special jobs large helicopters can be pressed into service, such as the one that hauled the mast onto the top of the CN Tower. Even despite everything there are still armies of workers putting things together far above the city streets, though they have much more portable safety equipment than their predecessors. The highest installation job ever attempted came at the very top of Burj Khalifa when a set of aircraft warning lights were mortared into the spire by hand.

Old fashioned ways stand out in the modern age, 330,000 cubic metres of steel reinforced concrete was poured correctly without flaws to make the Burj Khalifa, (39,000 tonnes of steel was used for the reinforcement), the kind of precision that could never be achieved before computer-aided design and control. The total amount of steel used in the building is roughly half the amount used in the frame of the Empire State Building, in a building twice the height. As always with concrete, time is of the essence. In Dubai the contractors had to order an entirely bespoke high pressure concrete pump design to get the stuff up to the top before it set. Reinforced concrete towers are made by 'Jump forming', following the lead set by great dams like the Hoover dam, where concrete is poured in blocks. In a tower instead of blocks for a dam wall there are floors; steel framework is lifted into place, concrete is poured around the frame, left to set, and when one floor is finished it becomes one side of the mould for the next layer. The outer mould 'jumps' up to next floor very twelve hours. Just like a giant dam wall exposed concrete towers like the German fehrnsehturm and CN Tower show the evidence of the forming in their surfaces, the lines of each level of forming still visible.  A big complication for construction in Dubai is the searing temperatures; The average summer day temperature can sit at well over the 30 degrees celsius, and concrete itself will heat up as it cures. Instead of applying some complicated refrigeration system to their concrete mixers the Burj Khalifa team took the uncomfortable but eminently practical solution of doing their pours at night.

Several major fires in the 1970s and 1980s brought the realisation that fire alarms and asbestos walls weren't going to cut it in such large buildings; far better to consider the whole structure. The MGM Grand fire in Las Vegas in 1980 showed how dangerous even minor fire could be in a large tower complex. The 'old' Grand, now the Bally's Casino, was built in 1973 with a tower attached to a low rise casino building next door. The fire began in an unoccupied busboy station in the casino, at seven in the morning. Even though the fire began far away from the hotel block 75 guests would perish from smoke inhalation, many in their rooms (there were 87 fatalities in total). The unchecked blaze sent toxic smoke up through staircases and through the seismic joints in the building, into the air conditioning system, into rooms and corridors. When the fire was out most of the casino had been destroyed but the hotel was largely intact, excerpt as rescuers and investigators discovered littered around were the eerie sight of deceased guests, many still in beds and chairs, some in corridors and stairwells, overwhelmed by fumes. The fire showed how important it was to compartmentalise the design of high rises to contain toxic smoke and to stop people accidentally sending themselves into mortal danger, even for something as innocuous as walking out to investigate a fire alarm.

Throughout history earthquakes were terribly damaging to cities built of wood, stone and brick. Steel at last offers some resilience thanks to its strength under both tension and compression, but skyscrapers are only as strong as the joints between the framework, and designers go to great lengths to ensure a building is strong and can flex under extreme stress without cracking. Though new York and Chicago, the two traditional hones of skyscrapers are relatively calm where earthquakes are concerned, there are plenty of places that are not so stable and are still packed with highrises. In the US both San Francisco and Los Angeles sit on the San Andreas fault, across the Pacific ocean on the other side of the ring of fire are Tokyo, Taipei and Kuala Lumpur. All these cities have prominent landmark towers that have proven their ability to withstand earthquakes and have some ingenuous design touches to aid their survival. San Francisco knows only too well the damage that can be caused by tremors. The earthquake of 1906 flattened the city, destroying nearly all the buildings on the center. The 1989 earthquake wasn't nearly as bad but still toppled a large stretch of double deck concrete highway in Oakland, a highway that had been built on softer water filled ground that amplified the shock waves

That earthquake caused no damage to the tallest spire in the city, the Transamerica Pyramid. The unmistakable triangular profile of the tower, with its two flanking wings peaking out of the top was designed to create less if an intrusive shadow over its neighbours, but it's shape makes it more stable. The building also has ingeniously designed interlocking panelling to keep all the window frames in one piece. The US bank tower is the tallest in downtown Los Angeles and was designed in 1989 in anticipation of the 'Big One' - the 8 magnitude shake that will one day come along the San andreas fault. Two decades later it hasnt arrived though the building survived the 1994 Los Angeles earthquake that caused widespread damage through the city. In Kuala Lumpur the twin Petronas Towers are connected by a high flying sky bridge that is hinged to allow the towers to slide along the bridge in a tremor. In Japan the Yokohama Landmark Tower sits on a system of rollers. It sounds a bit silly; a giant skyscraper sitting on rollerskates, but the principle is sound and the shock waves are dampened by such short system. 'Base isolation' as it is called, is actually an ancient idea dating back to antiquity, where stone buildings like mausoleums and temples were propped up on flexible bases to stop them crumbling down.The ultimate in earthquake proofing may be on Taipei 101 at the heart in the Taiwanese capital. Should the giant building fall over in a quake the damage would be extraordinary so the designers went to great lengths to ensure it doesn't. Stacked like a stack of baskets in a supermarket Taipei 101 is styled like a pagoda , turning the traditional lines of skyscrapers upside down. If looking at the building, and then looking at the view from the top of the
building are the top two sights in the city, then the sight of the huge stabilising mass damper in the roof may need the third most impressive sights. The 728 ton damper could be hidden from view but that would be like hiding the giant bells in a cathedral bell tower - quite unnecessary since visitors are keen to look at the device that keeps them safe if storms or earthquakes do strike. It does this by counteracting the forces pushing the building, as the building moves one way the damper, suspended in a cradle like a giant pendulum, stays perpendicular to the ground and brings everything back level. Mass dampers are standard issue to most modern skyscrapers. Taipei 101 earned its stars in an extraordinary way when an earthquake hit it while it was still under construction. Several construction workers were killed when a crane detached from the side and fell but the building was undamaged.

Earthquakes are an exceptional event for some skyscrapers, but all tall buildings face a constant battle against another natural force that provides potentially as much of a damaging threat as the ground shaking; the wind. Since the wind is invisible, we easily forget that effectively all city skylines are standing at the bottom of a giant sea of shifting air, and that air can move around with enormous force. Sticking large spires up into the wind is inviting disaster, partly for the obvious reason that strong winds could knock a tower over, but also for the lesser known problem that the building itself can generate forces that can cause it's own demise. The big boxy shape of the sears tower in Chicago is unlikely to be topped by a similar looking tower because of the forces of the wind. The 90 degree corners of the sears tower create air vortexes, just like the air spilling off the end of a plane wing that creates the contrails in a clear sky, the air passing around a skyscraper creates swirling Eddies of air, and areas of lower air pressure.

This lower pressure actually pulls the building backwards and forwards; the skyscraper isn't just on danger of being pushed over by the side wind but of shaking itself to pieces by the turbulence it creates. Or at least being unnervingly prone to swaying in the wind - The Sears Tower sways back and forth around fifteen centimetres from it's centre on an average day. Visitors remember the boxy World Trade Center towers doing something similar, as well as the howling wind down their lift shafts. Looked at closely the wtc towers give a small clue to the future of design - their corners were chamfered across to reduce turbulence around the towers and on each other. Big towers also create another problem in that they affect the wind around each other, so much
so that architects while building wind tunnel models of their own projects will also build the surrounding city and place everything in a wind tunnel to see what happens. Above five hundred metres the shape of the future is curved and aerodynamic. So well can a modern computer-aided design manage the impact of the wind that the Burj Khalifa can have outdoor terraces - hundreds of metres up - shielded from turbulent air with complex baffles that move like the flaps on an aircraft's wing, depending on the air flow over the building.

Lessons about the power of the wind had to be learned the hard way in the 1970's, when computer design was still it's infancy, and calculations were often still done with slide rules, pen and paper. The uneasy infancy of the Citicorp Building provides a cautionary tale to architects. The rakish headquarters of an American banking giant opened in 1977 in uptown Manhattan. From a distance the most distinctive feature was the slanted roof - intended for a huge solar panel array that was never installed. - but up close at street level the radical base stood out from anything built in the city before. Looking up from the street level the building seemed only to begin at the ninth storey, the whole perched atop the atrium and held up by four legs in the middle of sides, leaving the four corners suspended in mid-air, like a crossbreed of office tower and oil-rig. The design was dictated by the presence of a Victorian church occupying a corner of the lot. The agreement reached between diocese and bank was the bank could demolish the old church, as long as they built a new church on the intersection, and it was separate from their skyscraper. The engineers solution was to support the floors above by huge cantilever trusses attached to the central core and the four columns. The arrangement could have made for a very unusual and dynamic looking building, except the architect insisted on smooth white surfacing and clean lines, as befitting the clientele, and the surroundings, so all the engineering trickery was hidden under the skin.

All seemed normal with the building- just another Manhattan corporate headquarters, with an interesting gimmicky rooftop pinnacle - until the chief engineers office took a call from a graduate student. The 21 year old had been doing a project on the Citicorp tower and had wanted some information about the how the wind strength on the building had been calculated. Student and tutor were curious since they had been putting pen to paper working out from scratch the forces on the building and had come to the eye opening conclusion that very strong winds colliding at a diagonal angle onto the corners may be able to knock it over. Naturally this conclusion had seemed erroneous to the student, after all the tower had been standing for a year, open for business, on Lexington Avenue. Chief engineer of the project William LeMessurier came to an awful realisation. It was standard practice to calculate the effect wind had on a high rise by assuming it was striking the sides. Since all skyscrapers were rectangular boxes, firmly anchored at the corners in the ground, there was no particular reason to calculate the force on the corners. But the Citicorp was different; it's corners weren't fastened down, it was effectively a building standing on stilts. This would have been fine had the interior framework been firmly welded together, but since the maths had shown no abnormal wind loads on the sides the frame was bolted instead. And those bolts would pull apart and send the whole building smashing into its neighbours. The potential cascade of toppling skyscrapers that could result did not bear thinking about. The designer had accounted for some of the movement by installing a mass damper in the peak but he knew that the damper needed power to work and electricity was easily knocked out in a storm.

There followed an intense but highly secretive scramble to weld up the bolted joints and make the building strong enough to withstand high winds. And not just an extraordinary once  a century super storm, but given that the mass damper could not be relied on, the building was vulnerable to the kind of storm that forecasts showed happened on average in New York every twenty years. In fact there was already an Atlantic hurricane brewing off Florida. Had it stayed a course towards New York rather than swinging east back out into the ocean then upper Manhattan could have been in grave danger of turning into the world's largest game of dominoes. The emergency services were briefed and set on high alert of any storms and drafted plans to evacuate the whole area. Despite all the extraordinary measures being taken, all was kept secret from the public and even the Citicorp's occupants who continued to go to work everyday totally unaware of the controlled panic going on behind the scenes. Looking back from the age of 24 hour news and wall to wall social media coverage it seems amazing to think that word never got out and the secret of the emergency repairs was kept for seventeen years. The tower stood at the heart of America's news media empire, in a dense metropolis, but by coincidence all the city's newspapers were in the middle of a strike and not being published. Even the grad student who set the whole crisis in motion remained unaware. It was only in 1995 that a reporter for the New Yorker overheard the event being discussed at a party that the outside world was let in on the secret. And the anonymous student the chief engineer had always assumed was a young man turned out to be a 'she' - student Diane Hartley.

A building is only as strong as it's foundation. Without solid ground to stand on, great heights can never be reached. The granite bedrock underneath New York would seem to be a key ingredient in it's status as the world's hotbed of skyscraper construction but there is a little more to it than that. The bedrock of Manhattan island slopes down further south, so buildings in the Wall Street area have much further to go to sink their foundations than those uptown. For example the water level under the Woolworth Building was so high that it needed to use the same technique as the Brooklyn Bridge to create it's foundations. The bridge used giant sunken metal pressure vessels called 'caissons' to keep the Hudson River water out so solid pedestals could be laid on the bedrock. The same method simply moved inland to build skyscrapers. In places where earthquakes are common waterlogged soil needs to be stabilised to avoid "liquefaction"; the devastating loss of integrity caused by tremors that causes ground water to blow the ground apart, literally sinking buildings in slurry. In modern constructions polymer slurry is used to hold back water, turning wet ground into a treacle-like syrup where a concrete foundation can be poured and set. Where bedrock is near to the surface piles can be sunk to sit on the rock, though physics has an answer even where there is no rock. Modern skid-friction piles sit on nothing but soil, but can hold up thousands of tonnes. The ground 'pushes' back on the sides of the piles after all.

One of the most impressive of all foundations was the one built for the World Trade Center complex in the 1960s. Even before the skyscraper age there was so much demand for land in Manhattan that the island was pushing out into the surrounding rivers and land was being reclaimed from the water. The WTC was built on land that one hundred years before had been the Hudson river. The impetus for the project came from the New York Port Authority striving to bring investment back to the southern end of the island after midtown had taken prominence in the 1950's and 1960's. As always controversy was never far away as such a big project demanded public money from taxpayer and the removal of several blocks of low rise buildings housing local businesses and workshops. Looking back in hindsight the idea that such a valuable piece of real estate could ever have been a hotbed of electronic hobbyist stores called "Radio Row" seems almost quaint. After all in the 21st century, as the city gets ever richer and land gets pricier, even such iconic places as the Woolworth building have been sold off to new owners. The great gothic "Cathedral of Commerce" was sold by Woolworth's in 1998 and is now a private residential development. The majority ownership of the Chrysler Building is from Abu Dhabi. Sadly for the general public this means the ornate lobbies and observation decks, built to make giant buildings seem more welcoming and open, become off limits to casual passers-by. The writer Tom Wolfe called it, with a dash of satire, "kerbflash" - the knock out grandeur and pomposity of a great lobby - but after a century of skyscraper developments the fat cats ended up keeping the flash for themselves. So it was prescient in the 1960s for the World Trade Center to be conceived as a regeneration scheme and a way of bringing the public back to urban spaces.

The problem was that the soft reclaimed land at the tip of Manhattan was far from ideal to build huge steel towers on top of. The solution to the problem was the "Bath Tub"; a concrete box containing, subway lines, underground malls and car parking, that the towers could be built inside. After the towers collapse the city engineers were extremely concerned that the foundation structure was damaged by the immense impact on them and the walls would soon fail letting the river flood into the recovery area where the mountain of debris was being removed, and into the damaged subway tunnels. When all the structure was lifted away and the site cleared they found to great relief that the giant concrete shoe-box was still in one piece. In fact it seemed as eerily as though the past thirty years had never happened, and the army of heavy equipment was waiting to build the towers once more. With the reconstruction of the site and the new WTC rising from the ashes the foundation
has now been hidden again under the 9 11 memorial plaza, though with most of the memorial museum being underground the architects chose to leave large part of the concrete sides exposed on one wall, a tribute to the original construction work and also acknowledgement to its great strength and continuing function.

One new York "skyscraper" that has long been lost in the mists of time is the 1853 World's Fair tower. The temporary wooden observatory sat around where the new York Public Library and Bryant park is now, and was the tallest ever built at the time. In the shadow of the tower at the world's fair, inventor Elisha Otis first showed off his safety elevator. His innovation was a spring loaded ratchet mechanism that would hold the platform in place even if the rope snapped. Otis demonstrated this in dramatic fashion by being hoisted above a crowd and having his rope cut through. His demonstration platform would drop a few centimetres before the lack of force from the broken rope would release the safety ratchet, the ratchet locked into a toothed track beside the lift and held him steady. The creation of the steel frame was the key innovation in bringing forth the modern city but the invention of the lift was the spark that got it going. Winches and hoists have been around for millenia - a walk around the old centre of Amsterdam shows countless old townhouses with hoists out of the front gable for lifting things into the attic - but the safety elevator made it safe to put humans in a box and winch them up many floors. Otis was a pioneer of so-called 'fail safe' design; that is the safety mechanism that is always fixed on, until moving operation switches it off. So power failure or physical damage immediately switches braking systems on. The technology of lifts has moved on a bit since the 1870s but the principle is still roughly the same. It is just applied with more advanced materials and much more quickly. To avoid the kind of logjams that would mean office workers would spend half of their commute travelling up their own building lifts move as fast as more horizontal methods of transit. Taipei 101 takes the Guinness world record prize with its elevators speeding up and down at 60kph, taking passengers to the top in 40 seconds. As well as systems just like the original Otis safety lock lifts now have brake pads like racing car brakes, and huge cushioning systems at the top and bottom of shafts to catch either the lift car or its counterweight in the event of an impact.

Despite this accidents have happened, though usually it takes a dramatic outside intervention. Perhaps the greatest story of elevator mishap and miraculous survival was what happened to Betty Lou Oliver in 1945. Betty was a lift operator, and as far as lift operators go had the plum job in the Empire State Building. At 9:40 am on July 28th there was a sudden huge bang that rocked the building and threw her from the lift car. The reason for the emergency wasn't clear from the outside at the building was shrouded by fog but soon the news spread that an Air Force B25 bomber had smashed into the building. On a routine troop transit flight in the waning months of the war, the B25 had been heading for Newark Air Base, carrying only the three crew on this leg, before the low cloud had caused them to lose their way. La Guardia airfield had called them and advised them to divert from Newark to LaGuardia, but the plane continued over the city, turning blindly left roughly at the intersection of 42nd street and Fifth Avenue, and flying at 200mph straight in the Empire State's north side, close to the top. The plane had blown a hole in the side of the facade but in general building had stood up better than plane. It was a Saturday, but still many people were left trapped by fires waiting for rescue - a rescue that nearly killed Betty Lou Oliver. The fire crews instructed her to bring one of the remaining elevators back to the lobby, without realising that the plane's debris and fire had damaged the lift cables. Seconds after heading down the cables snapped clean through and the car suddenly started dropping down down the shaft. For a few terrifying seconds she fell, weightless, before the brake system came on, and fortuitously the severed lift cable came snaking down underneath the car and formed a huge spring in the shaft, also cushioning the impact. Still, it took several hours for the fire crews to dig through the debris to get her out. Eleven unfortunate people, including the three man crew were not as lucky, and didn't survive, the investigators placing the blame firmly on the planes commander for trying to fly so low over Manhattan in heavy fog, and at half the minimum recommended height. Radar and plane instruments would became much more advanced and it seemed as though the empire state crash would be an unfortunate one off.

As well as the obvious benefit if saving people's legs and breath trudging up staircases, lifts also turned the economics of buildings upside down. The street level had always been the most expensive to rent, for obvious reasons, they were next to passersby. With a lift the top floors suddenly became more desirable; as well as the pull of a nice view, they were usually quieter too, with the prestige of looking down on everyone else. Where once there was the attic, there was now the 'penthouse'. For big companies the model was set for profit, they could occupy a few lower floors in their corporate headquarters and rent out the top floors for top dollars. Though only seven floors, and perhaps not lofty enough to be called a skyscraper, the 1870 New York Equitable Life Building takes the credit for being the first building with the new passenger safety lifts. Only a few blocks away, many decades later the World Trade Center invented the concept of sky lobbies, taking inspiration from commuter railways and airport hubs to relieve the huge problem of overcrowding and getting people up and down a skyscraper with one hundred or more floors. Logically if there were enough lifts to service such a building then the entire construction would be filled with lift shafts. Not very efficient of course, so in the WTC there were a set of "big" lifts that stopped at the sky lobbies, where smaller lifts took people up the individual floors. The lobbies could be seen from the outside as the darker grey bands round the tower.

In the early days such elaborate and complicated buildings needed their own power generation. Electricity was a relative newcomer at the time, provided by a few small power stations. Pride came into it too; the entrepreneurs who built the early skyscrapers didn't want to rely on other people's services to make their headquarters habitable, but such large buildings needed a lot of juice, and plenty of water too. The Woolworth for example had coal stoked boilers, and four steam engines that exhausted up a giant chimney up the height of the building. There were other facilities too, like telephone lines, a safe deposit vault, a swimming pool, and it's own connection to then-brand new IRT underground railway line. As 'paperwork' increasingly became synonymous with office work there was more and more space to give over to filing. Some had entire lower floors full of filing cabinets. Such arrangements continued for decades, though steam power was replaced by more powerful diesel engines powering high pressure steam turbine generators; the 1929 New Yorker hotel had such a large DC electrical generator in its basement that the building didn't need join the national grid system till the beginning of the 60s and only because the old equipment was obsolete.

Now such self sufficient power has again come back into fashion with the rise since the 1980's of of the 'green' skyscraper as architects have tried to make their skyscrapers more efficient and less imposing on their environment. Once the tubular construction method and steel and concrete technology reached a point where any shape or style was possible and computer design could do the sums designers were free to bring in new ideas, and greatly increased complexity. Weaning buildings off the constant intravenous supply of electricity and water, and designing air conditioning, lighting, heating, and plumbing that takes advantage of  the surrounding environment was the major advance. Air conditioning is here to stay but instead of bolting ac units into offices the whole building can be designed with airflow in mind. The Burj Khalifa channels some of its naturally cooler air from the upper levels. The cross section is a three pronged star, the most stable arrangement in high winds and a design that allows all rooms to have external windows and natural light. Hundreds of gallons of condensation from the air conditioning system is harvested by the system and used to irrigate the artificial oasis garden and trees outside. Even elevators are getting more efficient, borrowing Kinetic Energy Recovery (KERS) technology from Formula 1 racing, to send heat energy from the lift's brakes into the building's electric power grid.

Most great architects are usually remembered for their whole body of work, skyscrapers included - Frank Lloyd Wright, Saarinen, le Corbusier, Norman Foster, et al. There were many great skyscraper architects of the early period, now remembered for their tall buildings above all else, the most well remembered name being that of Cass Gilbert, creator of several early skyscrapers, but mostly known today because of his association with the Woolworth Building. With this design Gilbert realised a way to make the building look even taller was add intermediate stages, to give the appearance of different boxes sat atop each other. Roman bridges, Medieval cathedrals and Victorian ironwork went up in stages because they had to, the load gradually spreading out across buttresses and arches. Steel frames didn't need to taper, or get lighter the higher they went, they just stood there as one solid unit. The problem was for architects looking to make an impression and show off how tall their creations were is that one solid block didn't look nearly as dramatic as a multi tiered spire. The new office towers were taller, but they didn't look much taller down on the ground because the watching eyes had nothing to focus on except a mass of windows and masonry. Without cues it is very hard for people to judge  scale, just like a huge power station chimney or a great redwood tree, a featureless building is hard to measure up. Architects like Gilbert and his fellows tried to use decoration to reintroduce that scale. Some with more success than others it must be said; across park square from the Woolworth in 1913 already built was the 1899 park row building a strange mishmash of Beaux-Arts flourishes that isn't flattered by its open and undecorated side walls.

Gilbert's Woolworth on the other hand still looks tall even today even though now it is far from the tallest building in lower Manhattan. As well its three sections, the building also emphasises the vertical lines, the windows being grouped together in rows, between four thicker columns drawing the viewers eyes upwards. The windows at the top of the blocks are styled slightly differently, there are shallow balcony like sections and the pinnacles on the top all adding the effect of height as well as the gothic style. These features could already be found around new York on smaller buildings; the cast iron facades of Soho tenement blocks showed off intricate Beaux-Arts detailing, a now draw many tourists uptown to see the remaining  blocks of these rare buildings; the 1898 Haughwought building on the east side is only five stories, but looks taller thanks to its strong vertical lines.
The designers also realised that the building needed to be impressive at Street level to passersby and made the bottom three levels into a huge atrium lobby. The lobby's most famous features were the gargoyles of some of prominent figures behind the buildings creation, Gilbert was depicted holding a model of the building and looking at it as if in contemplation. This depiction of him has probably been reprinted far more times in books and websites than his actual portrait and has probably added a great deal to people still remembering who designed the Woolworth.

The tall building mania that took over lower Manhattan quickly led to concern that some streets were being blocked from ever seeing direct sunlight. The old colonial roads were narrow, laid out in the age of stagecoaches and pedestrians and were now sat like mouse tracks next to the behemoths sprouting all around. Left unchecked the menace could take over completely. In 1916 the city acted with a decree that beyond certain heights all buildings must be stepped back from the street edge as they climbed higher. The Equitable building of 1915 is the skyscraper usually made the scapegoat for the new rules.Replacing the pioneering seven storey block from 1870, that was gutted by a fire, the new Equitable tower, built by Thompson-Starrett co, was a forty floor, U-shaped monolith, it's sides creating an artificial cliff 164 metres high straight up from the Wall Street kerbside. Since at this point Wall Street is barely two lanes wide the effect of the new arrival being an overbearing colossus was amplified even more (for comparison the Horseshoe falls at Niagara falls stand less than half the height at 57 metres top to bottom) Apart from over the entrance hall there was very little decoration on the building - there wasn't much point, it was impossible to get far enough away to see it.

City planners had something to gain too from restricting skyscrapers; tax money could be lost as overshadowed areas, since nobody wanted to build there. The 1916 Building Zone Resolution, or as it's better known the "Setback Rule", was the answer. The most obvious impact of the regulations was the effect of the rule that specified that for each foot the building was setback from the kerb line, five feet could be added to the height of the building. There was far more to it than this, but that was the basic idea. Large parts of town were zoned off limits to high rises, there were five main height zones, and the regulations also took into account the width of the street, with zones for that too. To allow freedom in some areas to build very tall towers one clause specified that if the tower area was less than 25 percent or of the ground lot, it could be as tall as the builder wanted. This rule explains the groupings of skyscrapers in lower Manhattan, midtown, and on the river fronts, and the low rise areas of SoHo, the East and Greenwich Villages, and uptown. It also explains the distinctive stepped back look of classic New York skyscrapers, as the building filled out the lot at the base, the stepped up in accordance with the regulations, before the thin tower spikes up to the pinnacle, like a giant steel and masonry wedding cake.

The new restriction had inadvertently given architects new possibilities with their designs. The Equitable and it's ilk were box like to maximise rentable inside space and the architects of these buildings had little to do except add flourishes onto the outside facade. Some with success; the Flat Iron's dramatic location was hard to beat, some with less success; the awkward Park Row building was one of many slightly odd looking mishmash of styles sitting around the city. By ordering that everyone had to make the buildings narrower the higher they went the architects were given free reign to play around and show off. 'Retro' design is nothing new or special to later decades. In the 1910s and 20s the architects of New York city borrowed heavily from other cities historic landmarks, much to the approval of their patrons, the heads of finance and industry who longed to have their own classically inspired creations, just as their predecessors built copies of colonnaded Greek temples and Palladian villas. The Metropolitan Life Insurance Building of 1909 was a facsimile of the Campanile of St Mark's square in Venice, only taller and wider of course. If Washington DC was a new Athens, then Manhattan itself, begun as Neuwe Amsterdam seemed to have fulfilled the destiny, and then some, becoming richer and more spectacular than anywhere in Europe had ever been. Not that they were confident enough to eschew traditions just yet.

French inspired "Beaux-Arts" still survived into the 1920s as did Gothic revival in both New York and Chicago with the distinctive pairing of the American Radiator building and the Tribune Tower. The latter had been designed via competition, offered in 1922 and won by John Howell and Raymond Hood. They came up with a building clearly influenced by gothic cathedrals in Europe, with buttresses and spiked crowns around a top that was only lacking the giant wooden spire. There was far from a consensus on the result in the industry and the press with a large number of critics and observers reckoning that Finnish architect Eliel Saarinen had  drawn up a more interesting form less reliant on traditional motifs. Saarinen would be the moral victor of sorts though since his design would be very influential on lots of 1920s high rises and his unsuccessful pitch for the Tribune building would spring up in several American cities including Detroit, Houston, San Francisco and Cleveland. Hood and Howell even borrowed much of it when they built the Radiator Building in new York, albeit their version was finished in black masonry. Taking the name of their client literally they finished the decorative flourishes in gold intending the whole to look like a coal fire.

Tastes always change and Gothic was on the way out and Art Deco was coming in, and with the changing seasons there would be some casualties on the way. Some of the grand buildings of the gilded age no longer exist. With its thin tower with a bulbous clock tower, the Singer Building looking a little like a large reddish brown tulip. It was dismantled in 1967, the tallest building ever to be taken down for commercial reasons. Perhaps it's odd appearance didn't help but this was not an auspicious time for preserving older buildings. In 1963 the original Penn Station was razed to create the Madison Square Garden arena complex. Train terminals, along with theatres and the old mansions of 5th avenue were becoming surplus to requirements in the age of the car. Penn station stayed in service but buried underneath "The Garden" as a mere commuter yard. Even worse than losing trade the Victorian age monuments were now old fashioned. It didn't help the Singer, a contemporary of Beaux Arts styled buildings, that it looked positively Victorian in styling. Grand Central Station would probably have followed Penn station had it not been for the general outcry at the prospect of its demolition. Even the former first lady got involved; Jackie Kennedy, now living nearby and an advocate for the new preservationists condemned as "cruel" the city being "stripped of all her proud monuments", with the a call to "reverse the tide, so that we won't all end up in a uniform world of steel and glass boxes". As it was the old terminal was saved but since the mid-sixties has stood in the shadow of the hulking PanAm building, a brutal slab of concrete that nearly everyone thought an eyesore, but that did promise a Jetsons style future with its rooftop helipad for quick commutes from the airports.

A similar thought had occurred to the planners of the 1920s, only they were thinking of giant dirigible airships as the vehicles for airborne commutes into the city. The idea was that instead of taking a car or train into town the well heeled could float into the middle of downtown. The real life counterparts of the fictional Jay Gatsby of the F Scott Fitzgerald's The Great Gatsby - who famously described the view over the Queensboro Bridge looking west at Manhattan as being the "first wild promise of all the mystery and the beauty in the world" - would disembark an airship at the top of a tower and ride an elevator to street level. Realistically it wasn't going to happen, and not just because as the great German airships were hydrogen filled timebombs that as the Hindenburg would prove were waiting to explode in flames, but airships could not be controlled precisely enough to moor with a solid building and needed ground crews to pull them in with guide ropes. Still the dream helped convince architects that there was more to the decorative spires atop skyscrapers than just hubris and decoration. When the Chrysler building beat 40 Wall Street to the title of tallest building the spire that was hoisted into place was entirely decorative and, like the spire of most cathedrals, hollow. Inside was a skeletal steel framework, and a ladder to allow maintenance. It looked good though and that was the main thing. As it was the headquarters of Chrysler stayed in Detroit, but if many cities would knock down some of it's earlier skyscrapers they would never dare with the Chrysler. The set backs up the building worked in perfect proportion with the spire. Though a gaudy design apparently based on overlapping hubcaps the whole worked so well because it was plated in stainless steel. Many architects chose gold or copper - The Woolworth had a gold pinnacle but over the years it faded. Copper weathered to green, but the Chrysler spire stayed unblemished. 40 Wall Street may have lost the title of world's tallest building even before its windows needed cleaning but it was still the tallest building in financial district. Nearby stood it's closest challenger, the City Bank-Farmers Trust Building (or 20 Exchange Place as it was eventually known). The full extent of the project was scuppered by the depression. It was supposed to be 258 metres tall, but ended up being a more modest 226 metres, albeit very skinny and elegant.

The Empire State may be an icon today but didn't make many friends when it was first conceived as it took over the site of the landmark Waldolf Astoria hotel. Never mind that the hotel moved a few blocks away to the giant palace like skyscraper that it occupies to this day, at the time the sight of a fine Victorian hotel having to give way to a giant office block sent many into howls of outrage. The design, by William Lamb of Shreeve Lamb and Harmon, is not the most dramatic and ornate, but makes up by being full of grandeur. The signature setback running down the centre of the building came about from designing the floors around the liftshafts, the architects favoured leaving no office too far from the elevators, so presto, the centre had a cutout. The proportions aged well over the years; the building is much wider than it is deep, giving it a powerful broad shouldered look. Had the sides been the same as the front and back it could have been too heavy looking. It also distinguished it's summit from the more flamboyant Chrysler building's symmetrical crown. There are many less less well known contemporaries that share the Art Deco style; 500 Fifth Avenue, built in the same year and designed by the same architects, looks like an assymetrical version of the Empire State, but as it nowhere near the same size, and does not command the centre of the city, it is relatively obscure. Like world famous rock'n'roll stars there are many imitators of the two buildings. While the Empire State has inspired with it's proportions, central negative-space cutout, and plinth at the bottom, the Chrysler's silver 'hubcap' spire has more obvious imitators. In Dubai passersby can be forgiven for thinking they are seeing double at the sight of the Al Kazim Towers, a pair of imitation Chrysler's standing side by side, with the aspect of a lego model copy of the original. More angular, crystal-like, modern takes on the telescoping spire became popular in the 1980s and 1990s, the most notable being the two towers of Liberty Place in Phildelphia, and the slightly less obvious Bank of America in Atlanta, and Prudential Plaza in Chicago. The most literal copy includes both of the iconic buildings together; the 'New York New York' casino complex in Las Vegas is a skyscraper hotel designed to look like the new York skyline of the 1930s, complete with Empire state and Chrysler building (further down the Vegas Strip The Eiffel Tower also has the honour of a Las Vegas recreation, though only at half scale of the original).

Under closer inspection Manhattan has other Art Deco gems. Built by the same architects as the Bankers Trust Building, the Cross & Cross company, and so thin it is practically an inhabited obelisk, the General Electric building boasts a dazzling spiked crown intended to evoke radio waves. The beautiful glass spire of 1932's 70 Pine Street was the one of last gasps of the Art Deco movement when it came to tall towers, though there would be one more great monument built in the 1930s before the depression bit hard into the ambition of builders and architects. As the 'Empty State' had proven there was no need for any more office spaces, and no desire to fund any more vanity projects when there were soup kitchen lines in many parts of town. Metropolitan Life Assurance had planned to supplement their 1909 campanile tower with a monster offspring next door, planned to have at least one hundred floors, but the depression saw to that. The project ended up being a handsome but squat thirty storey annex building. Now called '11 Madison' it is missing the monolithic stepped tower meant to built on top. No one knows quite how high it would have been; 100 floors takes the John Hancock Centre in Chicago to around 350 metres, whereas the roof of the Empire State is 381 metres with only 102 floors. Undoubtedly the newcomer would have tried to overtake the record holder and thus it would have been clearly the tallest building for decades instead. From the size of it's finished base it might have been the largest office block in the world even today.

By 1933 the only way to build tall in New York City was to be very rich and none were weather than the Rockefellers. John D. Rockefeller, the Standard Oil founder, was the wealthiest private citizen, by most measures, who has ever lived, (and, thanks to income tax and other 20th century inventions, probably ever will), and his son John D Jr, spearheaded a new skyscraper complex in midtown Manhattan  Much like the Woolworth building the project was entirely private, and named with a family name, mostly to attract tenants in the fallow Depression years. John D. Rockefeller Jr opened the Rockefeller Center in 1933, the elder Rockefeller did live to see the building open (he was 93 years old at time). The main building, designed by Raymond Hood of Howell and Hood, was not close to the Empire State and Chrysler in height and width, but it was very long, stretching across a city block, with the setbacks making it look like a large slab of slate chipped away down its corners. Inside it's slender profile made it airy inside; light from one side could reach across the aisle to the offices on the other side - as long as people left their doors open. Rockefeller was a self contained city within a city, and the family played the role of pillars of the community well, filling up the area with artwork, including the iconic "Atlas" statue at the foot of the main building. The complex contains the famous ice rink seen in countless movies, the 65 storey high Rainbow Room dining rooms and ballroom, television studios, and an underground shopping mall keeping the public right of way under the complex. There had been public atriums before, but the scale of the "Rock's" mall was unprecedented, and it's been copied around the world ever since.

The pure functionality brought about by the innovations of curtain wall glass and interior air conditioning reflected (often literally) in the aesthetics of the 1950s. After the long fallow period brought about by the depression and the Second World War, the world was ready for some new looks. The pioneering Lever House of 1952 set the trend: The headquarters of what is now called the UniLever corporation stands on Park Row in midtown Manhattan, and stood in stark contrast to it's masonry-clad surroundings, many now streaked in the grime and dirt of twenty years of city pollution. Lever House was built to the old 'setback' code, but instead of going for gaudy decoration and height the designers went for daring simplicity. The design boiled down to two rectangular boxes with scarcely any decoration, with walls of shiny reflective green tinted glass, criss-crossed by the thin grid of the window frames. The base box laid flat with the ground covering the lot, and complying to the building code, and the tower box stood offset at one end rising a decent but unshowy height. It is a look the world became so accustomed to in the years afterwards that it is hard to recall a time when it was new and radical. The "glass box" look became a big hit, and became known as the "International" style. Some older buildings were even retrofitted with glass curtain walls replacing the masonry.

For the first time the world was truly connected, and world governments now regularly met at the United Nations, in - of course - New York City. The United Nations building had really kicked off the trend for glass curtain wall buildings, even if it wasn't quite all-glass (the end walls were still stone- faced). For such a grand remit - the headquarters of a semi-official world government - the building had a grand competition inviting designs from all around the world, rather than just the traditional American architects. The age was all about scientific high tech, and many architects reveled in the purity of spirit, removing decoration and any ties to the past and local traditions and luxuriating in pure functionality and grandeur. The "modernists" like France's Le Corbusier imagined a return to the what some had imagined in the 1900s, with the great high rises becoming interconnected, offices linked by bridges high in the sky, and workers arriving from further afield by grand highways linked to "Unites d'Habitation" as the Frenchmen called his idealised ultra-modernist apartment blocks. The 'international' style was all about proportion: the proportion of the tower vs the plaza, the height of the roof space, the spacing of the windows. And none did it better than the Seagram Building, designed by Mies van der Rohe. The black and bronze tinted Seagram was widely imitated around the world. Van der Rohe got his proportions just right, so right in fact that it's easy to imagine that a big reason the International style eventually faded from fashion is that it was hard to top the Seagram building without thinking (literally) outside the box.

The new age was reflected in the new 1961 New York City building codes. These were even more complicated than before, with all kinds of exemptions and concessions, depending where a building was, whether it incorporated public spaces and other amenities and loads more besides, but the basic idea was that the setback rule was consigned to history and replaced with a floor to area ratio, essentially saying towers could go straight up again from the street as long as they weren't taking up too much of the lot. The rules have morphed and evolved since then, now including 'air rights'; letting developers build over the top of land owned by someone else who don't need a high rise but don't mind the money from selling the air above their land. Ironically once the rules had been set to accommodate Internationalism, the train began to come off the tracks slightly, and sometimes from unlikely sources. Walter Gropius was one of the great industrial designers in history, and his 'Bauhaus' school in Dessau, Germany had a incalculable influence on modern life, being the hotbed of modernist design. Even the Bauhaus studio building on it's own had a major impact on architecture, being a low-rise prototype for the glass curtain wall skyscrapers that arrived many years later. All the more surprising then that Gropius had credit in the PanAm building of 1963 that inspired outcry from New Yorkers. It didn't help that the monster stood off the grid pattern, at the top of Park Row, like a giant concrete canyon wall, dwarfing the older Helmsley building, and Grand Central Station in it's shadow. And it wasn't even all that original; even charitable critics pointed out that the building looked a lot like the Pirelli Tower in Milan, only larger and uglier. Ironically such was the pull of nostalgia by the early 1990s that when Pan American Airlines went bust and the building sold to the ubiquitous Metropolitan Life Insurance company the call went up from many to keep the "PAN AM" logo on the roof rather than replace it with "MetLife", (they didn't).

Housing tower blocks of the kind favoured by Le Corbusier and friends looked good on paper, but were often not put up with the same kind of care and quality of finish that applied to corporate headquarters. Some were literally falling apart; Ronan Point, a twenty two storey housing tower in the East end of London collapsed down one entire corner, killing four people, in 1968 when a gas line in a resident's kitchen exploded. Clearly a gas line catching on fire should not have blown apart an entire steel reinforced concrete building, and as investigators found, it hadn't; it had blown apart a concrete slab house of cards, built in a hurry and poorly fixed together. Even tower blocks that were bolted together properly were afflicted by "Concrete Cancer". Reinforced concrete, especially in wetter climbs, where water got in, the metal reinforcing corroded and split, the concrete came crumbling off and walls became a mess of unsightly rusty blemishes. The impersonal nature of modernism and great uniform glass walls had many detractors; "man is absent by his very accumulation" as the French philosopher Roland Barthes put it of the "a petrified desert of grids and lattices" in Manhattan.

Social anxieties were one thing, but internationalism did that thing that every creative style does eventually; it went out of fashion. Computers had a big part to play. Glass boxes were simple to build, like giant construction kits, but computer design allowed architects to really spread their wings. "Postmodernism" brought back superfluous decorative flourishes. Architects Phillip Johnson and John Burgee caused a buzz in 1984 with the New York AT&T Building (later Sony building, now 550 Madison Avenue), a fairly straightforward rectangular block with a pediment on its roof, making the whole look like an 18th century Chippendale cabinet. In Houston the Bank of America Center built a slab sided edifice with three ascending pinnacles that was part Rockefeller Center, part cathedral, part toast rack. The Dallas Bank of America lights up at night on it's edges in bright green neon-like electric outlining, as if inspired by the green on black computer monitors of the day. Some were even more unashamedly retro; the Wells Fargo Center in Minneapolis is as close a mimic of "The Rock" as can be found.The Peachtree tower in Atlanta is a copy of the 1920s Chicago Tribune Building, with added bulk. Another Bank of America tower, this time in Charlotte, was a straight-up Art Deco skyscraper, complete with glass crown; the Key Tower in Cleveland was built in 1991, not 1931, but the setbacks and terra-cotta finish owe everything to the latter decade. While these designs sprung up in smaller cities that only had a fleeting brush with the original 1920s skyscraper boom, and could be forgiven a little belated daydreaming, even New York had it's retro wannabees; the World Wide Plaza of 1989 was in style a 1930s Art Deco skyscraper, it even had a copper coated pyramid spire. Unfortunately economics dictated that it was fatter with more floor space than the originals and it's proportions caused widespread amusement and/or dismay. It has not been  helped at all by the 21st century revival of the originals. Cleaning, renovating, washing away the grime of decades, making places like 40 Wall Street, 70 Pine Street, and the General Electric Tower gleam again and look like new. Such awkward misfires led to a fading of postmodernism, it was a bit too "Disneyland" for many tastes. Style has evolved in recent years with the addition of a whole catalogue of the eastern architectural traditions of Islam, Hinduism, Japan, Korea, even influences from the natural world. Since the 1990s "international" wasn't just a style but a fact. While they incorporate the local vernacular the new Eastern skylines have been designed for the most part by Western companies. Skidmore, Owens and Merril of Chicago penned the Jin Mao building and Burj Khalifa. KPF of New York are responsible for the Shanghai Financial Centre and Hong Kong's tallest building the International Commerce Centre. Guangzhou, one of China's fastest growing skyscraper hotspots has it's own "International Finance Centre" - designed in London.

As skyscrapers aim to get ever taller there are the practical considerations of the wind and weather inspiring a trend towards organic and geometric forms, and some are bringing to life some of the more outlandish schemes left on paper for decades. With hindsight the abortive 1932 Metropolitan Life building proposal, would not only have put the Empire State in it's shadow, but with it's streamlined curving setbacks and bluff top, would have looked like being decades ahead of it's time. Students of history have noticed that the Burj Dubai looked not a little unlike the 'Mile High Tower', the fanciful 1957 proposal from Frank Lloyd Wright for the titular building a mile tall to stand in Chicago. It never came to fruition of course, Wright was eighty nine years old when he unveiled his vision, and died two years later, but nothing in the design was technically impossible, only exorbitantly expensive and unlikely to find any tenants. The Canton Tower in China looks very similar to the 'Hyperboloid', the plan that I.M. Pei had for the Grand Central Station site in the 1960s. The same architect would become world famous in the 1990s for the Louvre Museum pyramid in Paris, and the Bank of china building in Hong Kong, the former being a controversial but later widely lauded addition to a classical historic building, the latter being a highly distinctive skyscraper made from huge triangular trusses bunched together forming a unique shape - like a stack of pyramid shaped child's building blocks. Had history taken a different turn the I.M. Pei would have been known years earlier for the tower proposal that envisaged a twisting spire of circular segments climbing high criss-crossed by diagonal bracing. It would have been a beauty, as if a steel and concrete giant sequoia trunk had risen among the slab-sided status quo in Manhattan, but it would also have demolished Grand Central Station in the process. Somehow the two ideas; keeping the station while also building the much more graceful skyscraper behind it, never managed to come together, though they have in other places. London's icicle-like Shard, by Renzo Piano, may be Europe's tallest skyscraper (and one of it's most striking) but it sits atop and around older buildings around London Bridge station without requiring their demolition.

The mistakes and follies of the past have been learned from, and in the 2010s skyscrapers are no longer designed in isolation, they take into account their surroundings and occupants. The Shanghai Tower is divided into nine sections (or districts), an was conceived as a vertical city block, with sky gardens. An early example of more a holistic design approach is the 1997 Commerzbank Building in Frankfurt; the design endeavours to get as much light into the middle as possible, it has a triangular cross section, with a central atrium down the spine of the tower, and three indoor open 'sky gardens' connecting the corners. People in the middle of the building thus get a view down the middle of the building, as if they were looking outside, and some natural lighting. The psychological effect of big concrete and glass towers on their occupants has led to many designers trying to replicate something of the vibrancy of street life, to avoid an overly hermetic interior. The huge covered winter garden anchoring the three towers of the World Financial Center in New York stood in stark contrast to the empty open plaza of their former neighbour in the World Trade Center when they appeared in the late 1980s. Now the indoor garden is being transferred upwards; the roof garden is on the way back, there are acres of greenery hidden away from street level on the rooftops. "Vertical gardens" are panels of water soluble material running up the side of buildings that plants can grow up. The "Treescraper" is another idea that has been made real; the 'Bosco Verticale' in Milan is an apartment block coated in trees all mounted on balconies and parapets on the structure. The idea is ancient but the technology is cutting edge; the Hanging Gardens of Babylon brought back via the computer screen. New York may soon get the "Chlorophyll Tower", a tree-like structure designed to mimic the air and heat flow of a forest canopy for it's occupants in their individual apartment-pods. The advantages of bringing back nature are clear; cleaner air, bringing back long lost wildlife, natural insulation and temperature control, managing water runoff and flooding. The hard part, like all the other advances in skyscraper technology, is making it cost effective.

The treescraper may be the future, but style and height are still on the agenda; Some of the new tall apartment buildings going up in the new Manhattan boomtime in the 2010s have less concern with total floor space than if they were offices and have been able to bring back the thin spire skyscraper. The new '30 Park Place', a few doors up from the Woolworth Building, is in nearly all design aspects a 1920s building. Apparently the style had come back into fashion - maybe it looks more homely and warm as suiting a residential building compared to sheets of shiny glass. Though at the exact opposite end of scale is the Herzog and de Meuron designed 56 Leonard Street, this residential tower looks like a pile stacked glass boxes (or the "Jenga Tower" as it is already being nicknamed). At a complete right angle is the "Wave Building", or 8 Spruce Street, designed by Frank Gehry, with his signature styled rippling facade. In very similar vein - a skyscraper apartment building with natural design cues designed by a big name architect - is the 'Aqua' in Chicago, drawn by the late Zaha Hadid, the building very obviously sets forth a clear vision of a skyscraper built as if water is flowing down it's surface. Chicago has it's share of retro-modern setback towers too; the all-concrete Park Tower, and 311 South Wacker Drive could pass as creations of much earlier eras. Not that too many these towers house people who really live there all year round - they are "pads" at the most exclusive level, a place to stay in town at the weekend, some like the 8 Spruce Street building in New York are even rental-only. The occupants get the ultimate status symbol for the modern age, one that thousands of movies, television shows, songs, books and paintings have used as their subject matter.

The age of skyscrapers has coincided almost exactly with the age of cinema, both in time and location. The movie business boomed in America; next door to the new skylines rising and the former has used the latter as a setting since the silent age. Comedy star Harold Lloyd made the first famous use of heights when he dangled from a loose clock face above a street in downtown Los Angeles in 'Safety Last!' ... or at least appeared to dangle above the street. Movie magic meant a secondary platform underneath was kept out shot. In terms of duration the Empire State holds the record for having the longest starring role, though Andy Warhol's eight hour long 1964 movie Empire consists of nothing but the top half of the building filmed in real time from a camera set up on a rooftop a few blocks away. Though a footnote in the Warhol's work, and rarely screened, its supporters who have the patience to sit through the whole thing consider the film at least a prescient anticipation of Web cams and 24 hour security monitors.

Slightly more action packed was the 1933 cinema classic 'King Kong', the movie that put the three year old Empire State Building into pop culture legend. The giant ape that escaped from captivity and scaled the side of the building was in reality only 24 inches tall. Designer of models Willis O'Brien brought the scene to life through the laborious task of stop motion; moving the model for each exposure of the frame and animating the beast. The director intercut shots from the cockpits of the fighter planes sent to shoot king Kong from the side of the tower. Brand new technologies - double exposure printers, rear projections - combined with the models to produce unprecedented results, and practically invented the modern idea of special effects. After years of cinema spectacle usually relying on recreating historical battles, biblical scenes and adventures in exotic locations, this was a whole new kind of finale; fantasy meeting the real world the likes of which was normally stuck in the pages of books, and the super size skyline New York made the perfect backdrop.

1974's 'The Towering Inferno' is the most famous skyscraper movie, though the film itself did not age well and wasn't well regarded by many critics at the time. Several stars of the day passed on the Script, and the disaster movie trend died out quickly a few years later. The movie had some spectacular stunts and built several huge sets for interiors, though by modern standards the matte paintings used for backdrop and to make the San Francisco Bank of America building (used for the exterior of the fictional 'Glass Tower' tower) look much taller than reality are pretty obvious. And of course the subsequent events of 9 11 made the movie an awkward foretelling of real disasters to come. If movies celebrate the spectacle and grandeur of skyscrapers as a grand stage then they also bring to life some of their downsides, perhaps the most influential movies have been two set in the future; the 1927 German futurist vision 'Metropolis', and the 1982 Sci fi flick 'Blade Runner'.

Metropolis was conceived right in the middle if the German modernist movement, clearly taking influence from the new York skyline the 153 minute long silent picture scaled up the heights, added flying cars and bridges, and practically invented the futuristic city trope so familiar today.
In fact the film did borrow heavily from the writings and artwork of early Italian futurist Antonio Sant'Elia who had died in the Great War and never saw metropolis had proposed a multi level city, with pedestrian walkways, elevated trains and car highways, with elevators connecting them all. If the future was all about skyscrapers, then the Citta Nueva was the way to make it work. Though a little too fanciful many of Sant'Elia's less extravagant designs have stood the test of time well. What metropolis added was the more ominous aspect to the future that the rich would inevitably like literally at the top of the pile, while those nearer the bottom of the social heap disappeared in the shadows; the high rise city becomes a layer cake. The idea was taken up by Blade Runner's production designer Syd Mead, an industrial designer who brought a large dollop of realism to world of 2019 in the movie. In the future Los Angeles the newer and bigger buildings sit atop the older ones and the those on the rabbit Warren of dingy neon lit streets are swamped with the infrastructure required to support the higher ups. Those that are still on the planet though, as the really privileged have upped sticks and moved to the off world colonies. The huge Tyrel corporation lives in a giant mayan temple like monolith, shrouded in smog, and lit up by huge electronic billboards and thousands of glowing windows. The dark beauty of Blade runners future has been as influential as any real world cityscape - Syd Mead called sci fi design 'reality ahead of schedule', even if real city planners have been understandably cautious when it comes to proposals to put up huge LED screens on the side of buildings.

The Fox Building in Century City, Los Angeles, would be just another medium office tower if it wasn't for it's location close to Hollywood. It has appeared in many films and TV series though it's greatest starring role is undoubtedly in 1988's 'Die Hard' as the "Nakatomi Plaza", the skyscraper that gets taken over by Alan Rickman's German terrorist Hans Gruber with only Bruce Willis' cop John McClane on site to save the day. The movie is still regarded as one of the best modern action movies nearly thirty years later, as well as being the movie that swept away the one man army actioners of the 80s like Rambo, and putting the guns on the hands of more relatable everyman protagonists. The setting has a lot to do with this, where earlier action movies were usually set in foreign jungles and war zones, die hard had a major set pieces in lift shafts and offices, making full use of the surroundings that millions of people in the audience were familiar with to create now-iconic shootouts and cat and mouse games in offices and lift shafts. Now skyscrapers make frequent appearances in big budget action movies. The fact that they are easy to reach for film crews compared to wilderness and jungles, and large squared off buildings are comparatively easy to render in computer effects software probably helps matters. As do the incentives that local tourist boards throw at film companies to bring their production to town.

It's probably no coincidence that the rise of high rises in far eastern cities has coincided perfectly with their appearance in western movies. Entrapment, starting Sean Connery and Catherine zeta Jones as a pair of high class thieves puts the main set piece heist in the Petronas towers, opened a year before production started. In 2015's Fast and Furious 7 the two intrepid leads find that their robbery target is inside a hypercar, being kept by its owner at the top of one of the Etihad Towers in Abu Dhabi. Locations have influenced scripts since the beginning of cinema - the two heroes decide to jump the car from one tower to the other, but there are three Etihad towers so naturally their brakes don't work and they jump to the third tower too for good measure. The defining moment of skyscrapers in 2000s cinema, and cited as one of the best action set pieces ever created in any genre, comes in Mission Impossible Ghost Protocol as Ethan Hunt (Tom Cruise) and his team try time scale up the Burj Khalifa. Since the interior is crawling with goons they naturally have a plan to use their bag of movie technology tricks to climb up the side. The big selling point of the scene came in the production because cruise was actually put there, not clinging on with electromagnetic gloves, but roped up and climbing up the wall, facing the full force of the wind.

New York still rules the cinematic roost, thanks in large part to most of the world's comic book superheroes being based there (even if Batman calls the place 'Gotham', and Superman 'Metropolis'). At least Spiderman is named as living in the real big Apple, and naturally Peter Parker's Web slinging abilities find him making light work of the skyline, though 9 11 meant that the 2002 Spiderman had to abandon an ending where Spidey strings a Web between the two WTC towers. The marvel avengers also base themselves in new York, in the Canon of the comics and movies their Avengers Tower sits in midtown Manhattan. Quite why the superhero team base themselves rather prominently in the middle of a city rather than say, in a disguised desert island a la Thunderbirds, is up for debate. Aliens and monsters in movies really seem to have it in for New York; Independence Day's aliens blow up the Empire State Building first, the Cloverfield monster is set loose on the city, the Day After Tomorrow storm surge scours the streets, the 1998 version of Godzilla blew up the Chrysler Building - So being at the center of the action at least saves the Avengers having to travel far. The avengers tower is originally the Stark tower as owned by Tony stark, billionaire weapons developer and the creator of the iron man suit. In the original conics Tony bought up the met life building, chopped the top half off and put his own tower on top. Perhaps Tony built his tower on top of the met life because for aesthetic reasons New York building codes now outlaw giant logos to be displayed on the sides of new skyscrapers, so Tony could have his big 'STARK' sign because of the historical exemption granted the met life. Or perhaps being the egotist that his character is he couldn't resist the commanding view the site has down park avenue. In the movies the location was kept though the tower redesigned as a swooping asymmetrical shape with a helipad on top - Perhaps inspired by Burj al Arab hotel in Dubai, the D-shaped tower designed to mimic a sailboat on the waterfront, with it's protruding roof helipad.

Forty years after the original the producers of a remake of King Kong decided to switch the action to the World Trade Center, then only just finished. This version never really caught on in the same way as the the 1933 original; perhaps it was because the smooth sided towers looked so fundamentally un-climbable, perhaps it was the original story had a foreboding undercurrent to it that resonated with audiences of the depression era 1930s who had lived through the age of Rockefellers, Astors and Vanderbilts - the hubris of Americans travelling to Africa and unleashing disaster on the world's greatest landmark - in a way that didn't travel to the 1970s. It was the biggest starring role the WTC had, though it popped up time and again in establishing shots of sitcoms and movies. In March 2001 a briefly lived television series called "The Lone Gunmen" - a spinoff of the "X Files" about a trio of unlikely private detectives specialising in digging deep into murky government conspiracies, premiered with an episode centred around a spectacular insider plot fly a passenger airliner into one of the Twin Towers in Manhattan. The three heroes avert the plot - designed by the sinister conspiracy as an excuse to increase defense spending.

The movie world would meet the real world, with awful horrifying suddenness, on a clear late summer day, at 8:46 am September 11th 2001 For a vast number of people on the ground in New York, and watching on television news around the world the sight of a gaping, smoking hole in the side of the North World Trade Center tower was astonishing but as much a sign of a terrible mishap than something more sinister. A plane, that much seemed clear, but what kind of plane wasn't clear, or how it had ended up there. A blundering pilot or a collision, or technical problem perhaps? There were precedents to those who knew; the Empire State bomber crash of course, the 747 cargo jet that lost two engines and plunged into an Amsterdam apartment complex in 1992, destroying a whole building, and many the many crashes leaving and approaching JFK and La Guardia airports. The time it took for mindsets to change to a new world where great high rises could be in the crosshairs of murderous terrorists bent on destruction was a couple of hours. In the grim future that presented itself the question on all architects and engineers minds was how to possibly protect skyscrapers from planes being used as suicide missiles.

The towers had been targeted before in 1993, a truck bomb placed in the parking garage by Islamist extremists. Investigation and trial of the main suspect confirmed that the plan had been to knock one tower over into the other, and then into the rest of lower Manhattan. Somehow, the threat never quite took to the country's imagination the way it perhaps should have done, Two years later another terrorist, this time a radical American anti-government nationalist and militia member called Timothy McVeigh parked his rental truck right outside the front door of the Alfred Murrah Federal Building in Oklahoma City and walked calmly away without arousing suspicion. Minutes later, just as the working day was beginning, the truck exploded, blowing half of the reinforced concrete office complex into a smouldering pile of rubble. McVeigh's bomb killed 168 people, including nineteen children in a day cay centre, but, as structural engineers realised during their investigation, his device should not have been enough to cause so much carnage.  The reason it could was the same reason earthquakes can cause so much damage; the Murrah Building wasn't strong enough. And, more to the point, it wasn't required to be strong enough. It was built in the 1970s when building codes had much less stringent requirements, and "grandfather" clauses exempted it along the next two decades. The connections between the pieces had been blown apart by the bomb's shockwave, and most of the structure had been pulled down by the huge concrete lintel at the front falling over backwards.

McVeigh was executed in summer 2001, months before the September 11th plotters unleashed their brutally simple, but terribly destructive hijackings. The original designs for the Twin Towers had in fact considered the possibility of large jet aircraft hitting them, in the 1970s the default jetliner was the Boeing 707, a smaller size than the 767's that hit the buildings, but it wasn't the larger planes or the impacts that knocked out large sections of the external supporting columns that led to the collapse. Had the planes been running nearly empty of fuel the end results might have been different. The designers never took account of the huge fires fuelled by vast quantities of kerosene that that eventually melted the steel frame of the buildings enough for them to lose strength and give way. Unlike later tubular skyscrapers there was no concrete core, everything was made of steel, and the floors were very thin (around four inches). The 1970s-era fireproofing could not cope with a jet fuel fire, and neither could the sprinkler system. Eventually the whole structure gave way, falling straight down into it's foundation. Though the north tower was struck first it stood much longer than it's counterpart because it was hit much higher up. The South tower's damaged frame had to hold far more weight from above, and had been hit off-centre putting additional strain onto the damaged section and that gave way much more rapidly. Alas, though it held on  much longer, the size of the 767 and it's near right-angle impact, instantly blocked all the stairwells and lift shafts above the 91st floor of the North Tower, condemning every single unsuspecting soul above the first strike to their fate, including every patron and worker in the famous "Windows on The World" restaurant, for years the highest such place in the world.

For the more fortunate people lower down the towers stood long enough to evacuate but it was a slow procedure. Sadly the unprecedented nature of the disaster left many fatally unprepared for what to do. In WTC 2 many people stayed put or even went back to their offices, reasoning that it was safer to be inside than out in the plaza in the path of falling debris. When their building was struck many made their way up to roof, seeking a much shorter route to the outside and expecting rescue by helicopter as had happened in the 1993 bombing but that option never came: the heat and smoke pouring from the buildings made landing impossible. The offset hit by the second plane had left one stairwell passable and many of these victims could have made their way down but survivors reported that many of their fellows were put off by the fires blazing below in the stairs. A pattern seen before in high rise fires was repeated; those who went down and  braved the blaze and smoke made it through, while those who went up effectively found themselves inside a giant chimney. Even had the towers held up the chances are many would have been suffocated by the smoke before help arrived. Now designers consider smoke-proof refuge areas through the building a must in a super-tall tower.

2606 people were killed in the impacts, fires or collapse, 71 of them emergency responders.
Even after WTC 2 crumbled to the ground the New York Fire Department could not communicate with many of their units inside WTC 1 telling them to withdraw. The only sliver of comfort was for all the carnage the horror could have far greater, on a scale that would have been hard to comprehend. The towers could easily hold 17000 people on an average weekday. The early time of day spared the crowds of tourists waiting for the observatory in WTC 2 and many who had not yet started work. Some stories of escape from the day are testament to the tenacity of survival, good fortune, and selflessness from some helping others evacuate. Even some people on the floor directly under the path of the first plane made it out. Sixteen people from Stairwell B survived the North tower collapsing on top of them. The process of moving on from 9/11 took New Yorkers many years, years where there was still a gaping empty space in lower Manhattan, something not seen since colonial times, and politicians, city planners and architects argued over what should be there to replace the fallen towers. Daniel Liebskind's design chosen as the new World Trade Center, bordering the site of the original towers with a complex of five new buildings, a concept akin to the 1930s Rockefeller Center, but the odd-looking asymmetrical monoliths soon attracted derision, particularly the new centrepiece tower. Liebskind envisioned a tower with a huge spire of open glasswork, containing greenery and public spaces. Unfortunately the design of the spire made it very obvious that the actual body of the building was nowhere near the height of the original twin towers. Not the American Way at all, and the rather European-style caring, sharing, "green" tower didn't win many admirers among straight-talking New York stockbrokers, and power-brokers either. The drawing board was brought hastily back into action, and the designs of the various towers split off to different companies and designers, the only part of the original vision being the ground layout, and the central reflecting pools built over the footprint of the lost towers.

Part of the that healing process became the celebration of the extraordinary, and half forgotten story of Phillipe Petit, who in 1974 walked on a high wire strung between the two towers by him and a guerrilla group of confidantes, including a few insiders. He was a French circus performer, only 24 years old but already with several dramatic public stunts under his feet. The biggest was walking a high wire between the two bell towers of Notre Dame cathedral in Paris. "The Coup" as he called it, had been his long standing aim ever since he'd seen concept drawings of the towers in a magazine. The offset of the two towers meant that the wire was strung between the top right of the south tower and the bottom left of the North. The rigging was complicated; it had to cope with the winds, and still be portable enough to carry by hand and be put up on the fly at the top of the towers. It was a forty two metre walk across but a rather longer drop. In today's security environment it would have been impossible, no question, but it took some subterfuge back in the early 1970s too. They probably only pulled off the feat because the buildings were still under construction despite being partially occupied, so they could disguise themselves as workers and gain entry to places they shouldn't. Ironically when Petit stepped on a nail while in disguise the near disastrous injury to his foot proved a blessing. Standing on crutches people were so busy helping him through doors they never stopped to ask who he was.

Strangest of all was the mystery man who caught them in the act of putting up their rigging early in the dawn light but walked off wordlessly. It was one more piece of folklore in an event half lost in the passage of time; Petit crossed his wire above the artificial chasm several times, lay down, bowed, saluted the crowd looking up from the nearby streets, but nobody watching took a frame of moving film, leaving the event forever frozen in still photo frames. After attracting the attention of spectators and the police with his stunt, and experiencing what he described as an experience akin to flying, he climbed off to be quickly taken away by the NYPD. Though they could have held him on numerous trespassing and misdemeanour charges the city knew a folk hero when they saw one (the media had naturally gone nuts for the gravity defying French man) and merely ordered that he must do community service; by doing a tightrope show in central Park. In these more connected, risk averse and paranoid, times the story has charm because of its innocence, great spectacle and the fact that it can never be repeated. Even the man himself, still performing on the 21st century, still carries a lifetime pass awarded by the owners to the observation deck of WTC 2, now forever beyond reach.

Unlikely to see such a thing again, but the dark days when it seemed like skyscrapers might have no future are long past now, and for good reason. Money talks after all; as Woolworth Building designer Cass Gilbert said over a hundred years ago "a skyscraper is a machine that makes the land pay.” and the "haves" will always have the means and the method, as the rise of the new half empty supertall apartment tower shows all too well. Even modernism, the long lost art of less-is-more has crept back into fashion, except taking the unadorned monolith style skyscraper to startlingly slender constructions that almost dare the elements to push them over, or perhaps tempt the mere mortals to join their occupants at the floor-to-ceiling windows hundreds of metres up. Nothing it seems can stop the ancient dream to go big and tall, and now skyscrapers are undoubtedly tougher, and more secure than they were in the 1970s, even it does mean longer lines to get to the top. And nothing quite beats going up to the top and taking in the panorama, whether it's from a mountain pass or an observation deck. Astronauts call it the ‘overview effect’, the awesome realisation of scale of the view from space, looking back down on whole continents, and feeling both very small, and very large simultaneously. And since most of us are unlikely to make it into space, the elevator to the top floor, and the view, is the next best thing to make everyone a collosus for a day.