On September 11, 2001, four commercial passenger jet airliners were hijacked by nineteen al-Qaeda terrorists.
Two of the planes, American Airlines Flight 11 and United Airlines Flight 175, were crashed into the North and South towers of the World Trade Center in New York City. The hijackers then crashed American Airlines Flight 77 into the Pentagon in Arlington, Virginia. The fourth plane, United Airlines Flight 93, was originally intended to be crashed into the White House or the U.S. Capitol Building, but the passengers and crew fought back against the hijackers, causing the plane to crash into a field in Pennsylvania instead.
In total, 2,996 people were killed in the 9/11 attacks, including the 19 hijackers. It was the deadliest terrorist attack in world history and the deadliest aviation accident in U.S. history.
The 9/11 attacks also killed thousands of people who worked at or visited these sites or nearby buildings—including hundreds of firefighters who arrived at Ground Zero after being called away from their families on September 11; 343 police officers and firemen who died when one tower collapsed before they could evacuate; 343 Port Authority Police Department officers who were killed when their command center collapsed; 343 employees at Cantor Fitzgerald Tower who committed suicide rather than evacuate.