It has been a day filled with painful memories for thousands in the United States and around the world.
Two decades ago, hijackers seized three passenger planes and crashed them into the World Trade Center in New York City and the Pentagon in Washington DC. A fourth hijacked plane, believed to be intended for the US Capitol, crashed into a Pennsylvania field thanks to the heroic efforts of its passengers.
In all, nearly 3,000 lives were lost.
The formal ceremonies in honour of those who died in the carnage or while trying to save others caught up in it have now concluded.
Across the nation, Americans continue to commemorate this 20th anniversary and commit anew to "never forget" the victims.
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This coverage was brought to you by Holly Honderich, Sam Cabral and Joshua Cheetham, Ritu Prasad and Tom Geoghegan.