Lights begin to illuminate the National 9/11 Pentagon Memorial in Arlington, Va., as the sun sets Sept. 10, 2014. The memorial was created to remember and honor those lost at the Pentagon Sept. 11, 2001. 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.