Americans solemnly marked the 20th anniversary of 9/11 on Saturday, remembering the dead, invoking the heroes and taking stock of the aftermath of the deadliest terror attack on U.S. soil less than two weeks after the fraught end of the war in Afghanistan.

The ceremony at ground zero in New York began exactly two decades after the attack started with the first of four hijacked planes crashing into one of the World Trade Center's twin towers.

“It felt like an evil specter had descended on our world, but it was also a time when many people acted above and beyond the ordinary,” said Mike Low, whose daughter, Sara Low, was a flight attendant on that plane.

Her family has “known unbearable sorrow and disbelief” in the years since, the father told a crowd that included President Joe Biden and former presidents Barack Obama and Bill Clinton.

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