On 11 September 2001, the world watched in shock and horror as New York’s World Trade Centre Towers were reduced to rubble.
The Twin Towers were widely considered to be symbols of America's power and influence.
The attacks were carried out by nineteen men associated with Al-Qaeda who hijacked four airliners which they used to launch suicide attacks on the targets.
The attackers were from Saudi Arabia and several other Arab nations.
Two of the planes were flown into the towers of the World Trade Centre in New York City; a third plane hit the Pentagon just outside Washington, D.C.
The Pentagon is the headquarters of the U.S. Department of Defence.
A fourth plane crashed in a field in Pennsylvania.
Often referred to as 9/11, the attacks resulted in extensive death and destruction, triggering major U.S. initiatives to combat terrorism.
Over 3,000 people were killed during the attacks, including more than 400 police officers and firefighters.
It was the worst loss of life due to a terrorist incident on U.S. soil.