People who were too young on 11 September to even remember their lost loved ones, and others for whom the grief is still raw, have paid tribute with wreaths and the solemn roll call of the dead as America marked the 18th anniversary of the worst terror attack on US soil.
"Eighteen years. We will not forget. We cannot forget," Bud Salter, who lost his sister, Catherine, said at ground zero on Wednesday.
US President Donald Trump laid a wreath at the Pentagon, telling victims' relatives: "This is your anniversary of personal and permanent loss."
"It's the day that has replayed in your memory a thousand times over. The last kiss. The last phone call. The last time hearing those precious words, 'I love you'," the president said.
US President Donald Trump and first lady Melania Trump are joined by survivors, victim's families and staff as they participate in a moment of silence. Source: Getty Images North America
Later, former president George W. Bush, who was in office on 9/11, and then-Defense Secretary Donald Rumsfeld attended another wreath-laying at the Pentagon.
Near Shanksville, Pennsylvania, the third site where planes crashed on 11 September 2001, Vice President Mike Pence credited the crew and passengers who fought back against the hijackers with protecting him and others in the US Capitol that day.
"I will always believe that I and many others in our nation's capital were able to go home that day and hug our families because of the courage and selflessness of your families," said Pence, who was an Indiana congressman at the time. Officials concluded the attackers had been aiming the plane towards Washington.
Almost 3,000 people were killed when terrorist-piloted planes slammed into the World Trade Center, the Pentagon and the field in Pennsylvania.
After reading part of the long list of names, Parboti Parbhu choked up as she spoke from the ground zero podium about her slain sister, Hardai. Even after nearly two decades, "there's no easy way to say goodbye," she said.
Former US President George W. Bush participates in a wreath-laying ceremony at the 9/11 Pentagon Memorial. Source: Getty Images North America
By now, the heritage of grief has been handed down to a new generation, including children and young adults who knew their lost relatives barely or not at all.
Jacob Campbell was 10 months old when his mother, Jill Maurer-Campbell, died on 9/11.
"It's interesting growing up in a generation that doesn't really remember it. I feel a connection that no one I go to school with can really understand," Campbell said.
Like the families, the nation is still grappling with the aftermath of September 11. The effects are visible from airport security checkpoints to Afghanistan, where the post-9/11 US invasion has become America's longest war.
The aim was to dislodge Afghanistan's then-ruling Taliban for harbouring al-Qaeda leader and September 11 mastermind Osama bin Laden.
Earlier this week, Trump called off a secret meeting at Camp David with Taliban and Afghan government leaders and declared the peace talks "dead". As the September 11 anniversary began in Afghanistan, a rocket exploded at the US embassy just after midnight, with no injuries reported.
The annual Triibute in Light is illuminated on the skyline of lower Manhattan on the eve of the 18th anniversary of the 9/11 attacks in New York City. Source: Corbis News
Al-Qaeda's current leader used the anniversary to call for more attacks on the US and other targets.
In New York, Nicholas Haros Jr, who lost his mother Frances, reminded the audience of the al-Qaeda attackers and tore into Democratic Representative Ilhan Omar of Minnesota over her recent "Some people did something" reference to 9/11.
She tweeted on Wednesday that "September 11th was an attack on all of us."
The dead included Muslims, as Zaheda Rahman underscored after reading names at ground zero. She called her uncle, Abul Chowdhury, a "proud Muslim-American man who lived his life with a carefree nature, a zeal for adventure and a tenacity which I emulate every single day".
Others made a point of spotlighting the suffering of firefighters, police and others who died or fell ill after being exposed to the smoke and dust at ground zero.
A compensation fund for people with potentially September 11-related health problems has paid out more than $US5.5 billion so far. More than 51,000 people have applied. Over the (northern) summer, congress made sure the fund won't run dry.
