The Twin Towers were the tallest buildings in New York City. At 110 stories each, 1 WTC (North Tower) and 2 WTC (South Tower) provided nearly 10 million square feet of office space for about 35,000 people and 430 companies. For a brief period upon their completion in 1973, they were the tallest buildings in the world. They attracted roughly 70,000 commuters and tourists daily.

The towers were massive. The North Tower rose 1,368 feet—1,730 feet with a large antenna—and the South Tower stood 1,362 feet high. Views extended 45 miles or more from the top of the towers in every direction—far enough to see all five New York City boroughs, New Jersey, and Connecticut. Each weighed more than 250,000 tons and contained 99 elevators and 21,800 windows. Each floor was an acre in size and there was enough concrete in the towers to build a five-foot-wide sidewalk from New York City to Washington, D.C.

The towers had been the target of an attack before 9/11. On February 26, 1993, terrorists with links to an Islamist extremist group detonated explosives in a van parked underneath the WTC. Six people were killed and thousands were injured.