From Moscow to London, Oslo to Tirana, Europeans have signaled solidarity with Americans in spontaneous shows of mourning.
Across the continent, public events have been cancelled or postponed, as the magnitude of the horror sinks in. Flags are flying at half-mast, citizens have been signing books of condolence, and church bells have been tolling in mourning.
In recent months, the US and its traditional allies seemed to be drifting apart, amid European opposition to the Bush administration's defense and environmental policies.
Those differences have been put aside for now. "In the darkest days of European history, America stood close by us, and today we stand close by America," European Commission President Romano Prodi said Wednesday. "This criminal act was intended as an assault on all our shared values and on freedom itself. It is a true watershed, and nothing will ever be the same."
The European Union has declared today a day of mourning across the continent. Denmark is holding a national memorial service today, while Poland has cancelled all election rallies. Professional soccer has called off all its games this week across the continent.
In Britain, America's closest ally, thousands gathered yesterday for an unprecedented changing of the guards at Buckingham Palace. Britons joined Americans in what the royal family said was a sign of solidarity. One English woman told reporters "It is important that we are united at times like this."
Residents of Lockerbie, Scotland - where terrorists blew up a New York-bound airliner in 1988 - have sent letters of condolence to the mayors of New York and Washington. "We received comfort and support from America, following the Lockerbie air disaster," they wrote. "You are in our thoughts now and in the difficult times ahead."
Germans looked even further back, to America's aid to their country after World War II. Berliners held a march and service on Wednesday, while flowers continued to pile up near the cordoned-off US Embassy.
A sign there says simply: "Dear Americans, for years you were here for the freedom of our city; now ... we want to be there for you." In the nation's largest-circulation paper, the tabloid Bild, one German wrote, "as a little boy I received my first chocolate bar from the Americans."
Fire-fighters in many nations have held demonstrations of support for their US counterparts. Mourning bells have rung out in Austria and the Czech Republic, as elsewhere. Across Scandinavia, people observed a minute's silence, as did citizens in many nations across the continent.
Russia is among several countries to have launched blood-donor campaigns, and Russian security agencies have offered to help in the investigation. In Kosovo's capital, Pristina, tens of thousands demonstrated Wednesday in memory of the victims, many of them from Europe.
Britain estimates almost 100 of its citizens have died, and says hundreds more are still unaccounted for. Seven Italians are missing, and Portugal - which has declared two days of mourning - says three of its citizens are believed to have died, with 20 others missing.