TEN years on and the pictures are still scarcely believable.
Out of a clear blue New York sky came a day that would shape the century and give the world new shorthand for terror.
2,996 people died in the World Trade Centre’s two towers, more than 6,000 were injured and the images from that day will forever haunt America and billions around the world.
People from 70 countries were lost in the attacks including 33-year-old Nigel Thompson from Sheffield.
Nigel was working for bond traders Cantor Fitzgerald on the 105th floor of the south tower and was actually on the phone to his twin brother Neil, employed by another New York broker, when the first plane crashed into the north tower opposite him.
He was cut off shortly afterwards.
Thousands of stories of unbearable tragedy, heroism and dumb luck are being told all over again as the worst ever attack on American soil is remembered.
Even now 1,122 of the victims remain unidentified.
Jamie Midgley, son of Sheffield city councillor Pat Midgley, was living and working in the city at the time.
“I used to live and work in Brooklyn but on that day I was in Manhattan a training course on 34th Street,” said 42-year old Jamie who now lives in New Orleans with his American wife Jen.
“I was about two miles away from the World Trade Centre but I actually watched it unfold like most of the rest of the world – on TV. We didn’t go outside because we were near the Empire State Building and there were rumours that that might be the next target.
“People were calling me to make sure I was all right. I didn’t know anyone who got killed but I became aware that a lad from Sheffield had died.
“That night Jen and I went to the Brooklyn promenade with thousands of others and looked out over the city. There was still smoke and dust in the air coming from the ruins. The smell reminded me of Bonfire Night at home.
“I was very familiar with the World Trade Centre. Every time anyone visited from England I would take them to the top to look at the city.
“Two days after it happened we got stuck in an elevator on the seventh floor of a building and the fire service was called.
“It struck me that the men who released us would have lost friends and colleagues in the attack just hours before and there they were at a stuck lift two days later.”
Inevitably there are as many conspiracy theories about the attacks as there were casualties.
This week Dr Ian Crane, an outspoken believer in an even darker explanation for the tragedy spoke at Shiregreen Community Centre in Sheffield.
“We urge people to take responsibilty for their own knowledge and not rely on the media,” said the former oil industry worker.
“The official version of events just does not stack up. It was said that the steel structure was weakened by the fire but aircraft fuel cannot burn hot enough to melt steel. Something else brought the building down. It is the first and last time in history that a steel structured building has collapsed through fire. How is that?”
According to Dr Crane the atrocity was an excuse for the US to wage war in the Middle East and he speculates that forces within the US Government turned a blind eye to the threat or were actively involved in the attacks.
It used to be said that everyone could remember what they were doing when they heard that US President Kennedy had been shot in 1963.
September 11 was the 21st century’s first Kennedy moment.
New Yorker Rob Speranza had his moment watching events on TV in Sheffield.
“My dad used to work in that building, I had been there quite a few times over the years to see him,” said 37-year-old film maker Rob who moved to Sheffield in 1996 to study for a Phd at Sheffield University.
“He had moved to a new place a couple of years before but a lot of the people he used to work with were killed.
“None of my family or friends were involved but I was frantically trying to call everyone to see if they were safe.
“I won’t be watching a lot of the documentaries for the anniversary but I will be on my computer watching the New York Yankees play on Friday night.
“They will have a remembrance service before the game.”