US President Barack Obama has led the United States in remembrance of the 9/11 attacks, marking a 14th anniversary replete with echoes of that autumn day and the now perennial terror threat.
At 8:46am local time on the South Lawn of the White House, a bell chimed three times to mark the moment when Flight 11, piloted by al-Qaida operatives, careened into the North Tower of the World Trade Center in New York.
Crystalline blue skies and the hum of jet planes landing and taking off at nearby National Airport evoked that day of tragedy.
Obama and his wife Michelle stood solemnly beneath a US flag at half-staff, bowed their heads and marked a moment of silence.
The first couple were flanked by White House chefs, gardeners and housekeepers, as well as national security staff tasked with ensuring such an attack never happens again on American soil.
Evidence of 9/11's impact was everywhere - from Obama's stars and stripes lapel pin, now ubiquitous among US politicians, to the presence of Lisa Monaco, his homeland security adviser - a post that did not exist before the attacks.
Nearly 3000 people died on September 11, 2001 at Ground Zero in New York, at the Pentagon and aboard a hijacked airliner that went down in rural Pennsylvania.
"We honour those we lost. We salute all who serve to keep us safe. We stand as strong as ever," Obama later said in a post to social media.
Almost a decade and a half later, Osama bin Laden is dead and the US presence in Afghanistan and Iraq has ebbed, but Americans' sense of loss and shock has receded little.
In New York, police and relatives of those killed in the World Trade Center read the names of the victims at Ground Zero, now the site of the National 9/11 Memorial and Museum.
At the Pentagon, dozens of family members watched as Defense Secretary Ashton Carter placed a large wreath of white flowers.
"They did not and could not take from us what defines us," Carter said.