Photos from the 9/11 attacks and the immediate aftermath. Sept. 11, 2001, began as a Tuesday like any other and ended as a day we will never forget. Nearly 3,000 people were killed that day as al-Qaida airplane hijackers launched terrorist attacks on the World Trade Center and the Pentagon. That morning, the Twin Towers collapsed after two passenger jets -- American Flight 11 and United Flight 175 -- crashed into them, while a third -- American Flight 77 -- struck the Pentagon, causing damage. A fourth hijacked plane crashed into a field near Shanksville, Pennsylvania, as passengers aboard United Flight 93 learned about the other attacks and fought to retake control of the jet. Images tell the story of the day -- of heartbreak and shock, solidarity and determination.