The attacks claimed 2,973 lives, stunned the world, and unleashed the U.S. military's wrath from Afghanistan to Iraq.
The 67 Britons killed in the Sept. 11 attacks five years ago were remembered Monday at a memorial garden near the U.S. Embassy.
Before an early afternoon ceremony led by U.S. Ambassador Robert Tuttle, bouquets of white roses and yellow carnations were piled beneath the oak pergola where the names of the victims are inscribed on three bronze plaques.
Notes laid at the memorial were solemn reminders of what was lost the day when terrorist attacks on the United States killed nearly 3,000 people, including 500 people from 91 countries.
"You are not forgotten."
"I just want you back."
"Loved and missed by all your friends forever."
"Still in my heart."
Buried beneath the garden is a section of a steel girder from the wreckage of the World Trade Center. Above it, ivy climbs the canopy's pillars toward an inscription that reads, "Grief is the price we pay for love."
A note attached to a potted white rose bush reads, "To my dear friend, Michele. I can't believe it's been five years. You've missed so much and you've been missed so much. Love, Sue."
Thousands of British workers were expected to join in a moment of silence and to raise money for charities. Cantor Fitzgerald, the investment banking firm that lost 658 staff members at its offices above the 100th floor of the north tower, and the Boston Consulting Group, which split from Cantor, were donating global revenues from Monday's trading to charities, including a fund that assists victims' families.
About 120 police officers from across Britain traveled to New York to mark the anniversary along with Prince Andrew, whose flight to the United States was diverted the day of the attacks.
In Helsinki, at the EU-Asian summit, world leaders stood in silence Monday in memory of those who died.
"These horrific attacks clearly demonstrated that terrorism is a threat to all states and to all peoples," the EU said in a statement. "No cause, no grievance, can justify acts of terrorism."
Japanese Prime Minister Junichiro Koizumi warned that terrorism remains as big a threat as ever, while Australia's leader promised that the values of liberty and religious freedom would in the end emerge victorious.
U.S. and Philippine troops fighting Islamic extremists in the jungles of Southeast Asia prayed for peace and safety, as other remembrances took place in Finland, South Korea and Thailand.
In Manila, one group marked the anniversary with a rally near the U.S. Embassy, carrying signs and chanting slogans accusing the Philippine and U.S. governments of being the "real terrorists."
Al Qaeda reportedly released a video tribute to the planning of the attacks on New York and Washington, which killed nearly 3,000 people, while the terror network's No. 2 leader, Ayman al-Zawahri, called on Muslims to step up their resistance against the U.S.
Hardline lawmakers in Pakistan blamed the five-year U.S. counterattack for "destroying peace in the entire world."
Monday's outpouring of emotion reflects an international landscape vastly changed since terrorists hijacked four airliners in 2001, crashing two into New York's World Trade Center, one into the Pentagon and another into a Pennsylvania field.
In the first of at the three crash sites, and first lady Laura Bush stood in somber silence Sunday after laying wreaths where the twin towers of the World Trade Center once soared. He later pledged "renewed resolve" to remember the lessons of Sept. 11.
Halfway around the globe, Australian Prime Minister John Howard echoed the determination at a ceremony Monday held at the U.S. Embassy in Canberra, saying "terrorism is the enemy of all people of good will."
Howard branded the Sept. 11 strike "an attack on the values that the entire world holds in common" and promised that the ideals of liberty and freedom of religion and speech "will in the end triumph."
Another memorial ceremony was planned at the U.S. Embassy in Tokyo, which has sent troops to Iraq and aided in logistics support for operations in Afghanistan.