The September 11 attacks - which were described as a " watershed moment " of contemporary history - were a series of coordinated suicide attacks by Al-Qaeda upon the United States on 11 September 2001 . On that morning , 19 Al-Qaeda terrorists hijacked four commercial passenger jet airliners . The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City , killing everyone on board and many others working in the buildings . Both buildings collapsed within two hours , destroying nearby buildings and damaging others . The hijackers crashed a third airliner into the Pentagon in Arlington , Virginia , just outside Washington , D.C . The fourth plane crashed into a field near Shanksville in rural Somerset County , Pennsylvania , after some of its passengers and flight crew attempted to retake control of the plane , which the hijackers had redirected toward Washington , D.C. Major terrorist events after the 11 September 2001 Attacks include the Moscow Theatre Siege , the 2003 Istanbul bombings , the Madrid train bombings , the Beslan school hostage crisis , the 2005 London bombings , the October 2005 New Delhi bombings , and the 2008 Mumbai Hotel Siege
September 11 attacks
September 11 attacks
Contemporary history