A ceremonial U.S. flag is unfurled over the side of the Pentagon in Arlington, Va., Sept. 11, 2014, at sunrise in commemoration of 9/11. Terrorists hijacked four passenger aircraft Sept. 11, 2001. Two of the aircraft were deliberately crashed into the World Trade Center in New York; one was crashed into the Pentagon; the fourth crashed near Shanksville, Pa. Nearly 3,000 people died in the attacks.