On a grey autumn day in London, workers and tourists alike line up in Grosvenor Square to pay their respects to those who perished.
After passing through strict security - where even the floral tributes are scanned - they sign condolence books and lay flowers around the statue of the late US president, Franklin D Roosevelt.
It is an enormously affecting place to be. Among the British people sending messages of sympathy and support - some waiting anxiously for news of missing loved ones - are Americans stranded a long way from home.
Many are inconsolable, some are angry as well as upset. Strangers hug each other for comfort and exchange stories about their loved ones back home.
Tears stream down the face of Norma Jean Cohn, a Californian who works for American Express in London, as she waits to go through the security checks.
"Twenty of our colleagues who work in the World Trade Centre are still missing. They worked on the 26th floor of Tower One but were up and down it all day for meetings," she says.
Her bouquet of red roses bears a simple message: "God bless America, land that I love."
Quite overcome
New Yorker Karen Digiacomo is holidaying in the UK with her mother, Carol. They were due to fly back on Thursday, but all US-bound planes have been cancelled.
"We just want to go home. We heard about the attacks from a salesgirl in Harrods and headed straight down to the TV department.
"I work across the street - what used to be across the street - from the twin towers. There's a lot of people I work with that I think are alright."
Carol Digiacomo adds: "We have policemen and firemen in our family who were called in to help. We've finally managed to get through to them, and everyone is OK."
Stand together
The word from home is that New York is now a very silent city.
"People are just walking the streets stunned," Carol says, her voice cracking with emotion. "I think our lives have changed forever."
Among the Britons paying their respects on Thursday were former Prime Minister Margaret Thatcher, London mayor Ken Livingstone and Camilla Parker Bowles.
Also in attendance were members of the London Fire Service in formal uniform.
After laying a large bouquet at FDR's feet, a sombre firefighter crossed himself in memory of his American counterparts buried in the rubble of the World Trade Center.
Jeffery and Maria Wilcox, of Los Angeles, say they have been deeply moved by the tributes.
"This is probably the most binding scene of world unity I've seen in my lifetime. I can't thank the British people enough for all their support," Mr Wilcox says.
Susanna, an elderly London resident comforting the tearful tourists in Grosvenor Square, says she came to do what little she could for the bereaved.
"Whatever you write, please send them my love."