<P> On a typical weekday 50,000 people worked in the towers with another 200,000 passing through as visitors . The complex was so large that it had its own zip code: 10048 . The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower . The Twin Towers became known worldwide, appearing in numerous movies and television shows as well as on postcards and other merchandise, and became seen as a New York icon, in the same league as the Empire State Building, Chrysler Building and the Statue of Liberty . The World Trade Center was compared to Rockefeller Center, which David Rockefeller's brother Nelson had developed in midtown Manhattan . </P> <P> One World Trade Center and Two World Trade Center, commonly the Twin Towers, the idea of which was brought up by Minoru Yamasaki, were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls . They were the main buildings of the World Trade Center . The North Tower (One World Trade Center), the tallest building in the world at 1,368 feet (417 m) by the time of its completion, began construction in 1966 with the South Tower (2 World Trade Center); extensive use of prefabricated components helped to speed up the construction process, and the first tenants moved into the North Tower in December 1970, while it was still under construction . When completed in 1973, the South Tower, Two World Trade Center (the South Tower) became the second tallest building in the world at 1,362 feet (415 m); the South Tower's rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high . Each tower stood over 1,350 feet (410 m) high, and occupied about 1 acre (4,000 m) of the total 16 acres (65,000 m) of the site's land . During a press conference in 1973, Yamasaki was asked, "Why two 110 - story buildings? Why not one 220 - story building?" His tongue - in - cheek response was: "I didn't want to lose the human scale ." </P> <P> When completed in 1972, 1 World Trade Center became the tallest building in the world for two years, surpassing the Empire State Building after a 40 - year reign . The North Tower stood 1,368 feet (417 m) tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood 362 feet (110 m) tall . With the 362 - foot (110 m) - tall antenna / mast, the highest point of the North Tower reached 1,730 feet (530 m). Chicago's Sears Tower, finished in May 1973, reached 1,450 feet (440 m) at the rooftop . Throughout their existence, the WTC towers had more floors (at 110) than any other building . This number was not surpassed until the advent of the Burj Khalifa, which opened in 2010 . Each tower had a total mass of around 500,000 tons . </P> <P> Although most of the space in the World Trade Center complex was off - limits to the public, the South Tower featured two public viewing areas called Top of the World Trade Center Observatories: an indoor one on the 107th floor and an outdoor one on the roof . Visitors would pass through security checks added after the 1993 World Trade Center bombing, then were sent to the 107th - floor indoor observatory at a height of 1,310 feet (400 m). The exterior columns on each side of the floor were narrowed to allow 28 inches of window width between them . The Port Authority renovated the observatory in 1995, then leased it to Ogden Entertainment to operate . Attractions added to the observation deck included a simulated helicopter ride around the city . The 107th - floor food court was designed with a subway car theme and featured Sbarro and Nathan's Famous Hot Dogs . Weather permitting, visitors could ride two short escalators up from the 107th - floor viewing area to an outdoor platform at a height of 1,377 ft (420 m). On a clear day, visitors could see up to 50 miles (80 km). An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing and leaving the view unobstructed, unlike the observation deck of the Empire State Building . </P>

How many stories in the world trade center