World Trade Center site
On the morning of September 11, 2001, Islamic terrorists affiliated with Al-Qaeda hijacked American Airlines Flight 11 and United Airlines Flight 175, both which were en route to Los Angeles, and intentionally crashed them into the two main towers of the World Trade Center. The towers collapsed within two hours of the collisions. 2,606 people, including 2,192 civilians, 71 law enforcement officers, and 343 firefighters, who were in the towers and in the surrounding area died in the attacks, as well as 147 civilians and the 10 hijackers aboard the two airliners. After the collapse of the World Trade Center, hospital workers and law enforcement officers began referring to the World Trade Center site as "Ground Zero".
Hijackers in the September 11 attacks
The hijackers in the September 11 attacks were 19 men affiliated with al-Qaeda. 15 of the 19 were citizens of Saudi Arabia, and the others were from the United Arab Emirates (2), Egypt, and Lebanon. The hijackers were organized into four teams, each led by a pilot-trained hijacker with three or four "muscle hijackers," who were trained to help subdue the pilots, passengers, and crew.