On 11 September 2001, a series of coordinated terrorist attacks were carried out by the extremist group al-Qaeda* against the United States.
Two hijacked planes crashed into the Twin Towers of the World Trade Center in New York City, causing the buildings to collapse and another plane hit the western part of the Pentagon near Washington, DC. The fourth hijacked aircraft was forced by the passengers to crash-land near the city of Pittsburg in the state of Pennsylvania to prevent it causing any more civilian death.
Nearly 3,000 people were killed in the attacks, including passengers and crew members on the planes, office workers, and emergency responders.
Take a look at rare photos of the terrorist attacks in Sputnik's gallery.
*A terrorist group outlawed in Russia and many other countries.