On 11 September 2001, a series of coordinated terrorist attacks saw almost 3,000 people lose their lives.
Four airplanes were hijacked by Al-Qaeda suicide bombers, with one crashing into the Pentagon in Washington and another in a field in Shanksville, Pennsylvania.
The other two passenger jets were directed at the two towers of the World Trade Center in New York.
Some of the photographs taken that day have been etched into our memories.
Here are the stories behind some of the most iconic images.
The Falling Man
Perhaps one of the most lasting photographs from 9/11, it was taken at 9.41am and shows a person moments after they had leapt out of a window.
The name of the person in the picture is still not known, though it's believed he worked at a restaurant inside the North Tower.
Photographer Richard Drew, who captured the image, told The Daily Beast: "For me, it's a very quiet moment.
"It's not a violent picture in any way.
"I think some people are turned off by this picture because it could be their fate.
"But it's not a part of this man's death, it's a part of his life."
Marcy Borders - 'Dust Lady'
Marcy Borders was just 28 years old at the time of the attack, working on the 81st floor of the North Tower.
Stan Honda took the photo of her that has been seen the world over, covered head to toe in a thick layer of dust.
Marcy was later diagnosed with cancer and suffered badly from depression.
Sadly, she died in 2015, aged just 42.
She once told The Jersey Journal that she blamed her illness on 9/11 after having inhaled so much debris.
She told the publication: "I'm saying to myself, 'Did this thing ignite cancer cells in me?'
"I definitely believe it, because I haven't had any illnesses. I don't have high blood pressure... high cholesterol, diabetes. How do you go from being healthy to waking up the next day with cancer?"
When she was asked whether she looked at the photo of her from that day, she said she didn't.
"I try to take myself from being a victim to being a survivor now," she said. "I don't want to be a victim anymore."
Edward Fine was just about to step foot in one of the lifts on the 79th floor of North Tower when the plane struck.
Believing it was a bomb, he raced downstairs and, luckily, made it out alive just as the second plane hit.
Recalling his experience, Edward later told The Today Show that, at the time, he was just concentrated on surviving.
He said: "I was focused in on: I must get uptown, I must keep surviving, I must walk.
"And I wasn't looking or thinking about anything other than surviving."
But while the attack left a deep, indelible scar on many people's lives, Edward decided to focus on the positives.
In an interview with The Mirror, he said: "My story is a very positive story.
"Once I got out I was never depressed. I think about how lucky I was. But I feel terrible for those who did not survive."
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