People are reliving the moment they realized a plane had flown into the North Tower on September 11, 2001.
Many are sharing their experiences on Twitter alongside the hashtag "where were you."
The most chilling accounts come from those who were too young to understand the harrowing events unfolding in New York City — and the teachers who had the impossible task of keeping themselves and their classes calm.
Some were working when the news broke.
Others were ready to go to war.
There were those who lived a frighteningly close distance to the World Trade Center.
And those who weren't even in America, but felt the shockwaves all the same.
And me, I was in school. I don't remember much, only the American teaching assistant breaking down in uncontrollable sobs. I was too young to grasp the reality of it.
Services were held across the world to mark the 15th anniversary of 9/11.
President Obama led a moment of silence at the White House at 8:46 am. The day before, he said,
We're still the America of heroes who ran into harm's way, of ordinary folks who took down the hijackers, of families who turned their pain into hope. We are still the America that looks out for one another, bound by our shared belief that I am my brother's keeper, I am my sister's keeper. In the face of terrorism, how we respond matters.
In New York, Hillary Clinton had to leave a memorial service early after she became unwell.
A statement by her campaign read,
Secretary Clinton attended the September 11th Commemoration Ceremony for just an hour and thirty minutes this morning to pay her respects and greet some of the families of the fallen. During the ceremony, she felt overheated so departed to go to her daughter's apartment, and is feeling much better.