The World Trade Center consists of two 110-story office towers.
Architect Minoru Yamasaki designed the outside skin of the World Trade Center as a steelwork of mesh that supported a large proportion of the building's weight.
The World Trade Center buildings are New York's tallest skyscrapers.
At peak periods of construction, some 3,500 workers were on the site daily.
With 60,000 tons of cooling capacity, the World Trade Center's refrigeration plant is the largest in the world.
On Feb. 26, 1993, a terrorist bomb exploded in the World Trade Center, carving out a 200-foot-wide, five-story-deep crater in building number one's lower levels.
One of the towers is just 6 feet taller than the other.
The French aerialist Philippe Petit walked on a tightrope suspended between the twin towers in 1974.
It is possible to see 45 miles in every direction from the observation decks.
Some 40,000 people work in the World Trade Center. More than 150,000 business and leisure visitors come to the complex each day.
