The ringing of solemn chimes at 8:46 am (1246 GMT) Sunday at the new National September 11 Memorial marked the anniversary of the beginning of a terrorist attack on the United States that has shaped world history over the past decade.
That was the exact time 10 years ago that hijacked American Airlines flight 11 was crashed into the north tower of the World Trade Center, followed just 17 minutes later by United Airlines flight 175 into the south tower.
U.S. President Barack Obama and former president George W Bush were attending the ceremony, the first time the memorial has been unveiled to the public.
It consists of walls of water rushing into two pools that define the footprints of the two towers, which crumbled to the ground in fiery disaster after the attacks.
A total of 2,977 people died on September 11, 2001, most of them at the World Trade Center. Two other planes were hijacked within little over an hour of the first attack and crashed into the Pentagon and a field in Shanksville, Pennsylvania.
Their names, along with six names of those killed in the failed 1993 terrorist attack on the World Trade Center, are engraved on the outside of the walls.
