This day known as 9-11 is one of the most tragic days in history, and if you don’t know why I will tell you.. On September 11, 2001 In NYC Lower Manhattan. 19 terrorists from the Islamist extreme group al Qaeda hijacked 4 commercial aircraft planes. Each contained approximately 76 passengers, 11 crew members, and the hijackers. 1 of the planes crashed into Arlington, Virginia. And the other one in Western, pennsylvania.