"It's hard to be here, it's all coming back now," the 39-year-old carpenter whispered, watching 24,000 family members walk down a ramp to lay roses and plant flags into the dry, brown dust at ground zero, now considered a Manhattan cemetery for 2,800 people. "You just can't forget it."

A year ago, when he saw the planes hit Manhattan's silver twin towers, Mr. Nolan packed his jeep with shovels and picks and sped to the ruins to dig for survivors. For weeks, he sifted through debris and cut apart steel girders that glowed red.

"It was a war zone. There were body parts everywhere. Nobody said much. Guys you knew for years would make eye contact and say nothing -- we knew we were all thinking the same angry things.

"But I'm here today, with my wife and my boys," he said, nodding at four sons who clung to his legs. "I want to show them that it's safe now and their dad will be rebuilding Manhattan."

Across the United States and around the world, millions paused for similar moments of reflection on the terror attacks, when the world changed in an instant.

U.S. President George W. Bush, his eyes sometimes wet with tears, led his country in prayer ceremonies that began at the Pentagon, pledging that "today we remember each life."

"Though they died in tragedy, they did not die in vain," he said, clenching his fist.

"Their loss has moved a nation to action in a cause to defend other innocent lives across the world. . . . As long as terrorists and dictators plot against our lives and our liberty they will be opposed by the United States Army, Navy, Coast Guard, Air Force and Marines."

In other countries, commemorations ranged from the secular to the spiritual, and were accompanied by declarations of friendship and shared principles from world leaders.

In Rome, the Vatican held a special mass in the basilica and Pope John Paul II used his weekly audience to condemn terrorism under any guise. "No situation of hurt, no philosophy or religion can ever justify such a grave offence on human life and dignity," the Pope said. "Let us pray for the victims to rest in peace and may God show mercy and forgiveness for the author of this horrible terrorist attack."

Parisians watched two bright beams of light reach into the sky, symbolizing the twin towers. London's St. Paul's Cathedral dropped thousands of rose petals from its dome, each one representing a life lost on Sept. 11. In Australia, 3,000 people wearing red, white and blue shirts stood on a beach and formed a U.S. flag.

Not all marked the day solemnly, however.

Islamist militants gathered at a mosque in London's Finsbury Park to discuss the "positive outcomes" of the attacks. In a meeting called "Sept. 11, 2001: A Towering Day in History," they said al-Qaeda had a "rational justification" for the attacks, but denied having ties to the terror network.

In Baghdad, where the regime of Saddam Hussein fears an invasion by the United States, the Al-Iktisadi newspaper ran a photograph on its front page of the burning towers with a headline that translated as "God's punishment."

That by no means defined the views of the Islamic world. At mosques from Manhattan to Kuwait -- whose government ran ads of condolence in The New York Times -- prayers were read from the Koran.

Russian President Vladimir Putin told Mr. Bush in a telephone conversation: "In Russia, we say that time heals everything, but there are things we cannot forget and which must not be forgotten."

At the United Nations, where Mr. Bush will appear today to present his case for military action against Iraq, Secretary-General Kofi Annan declared, "There could be no greater affront to the spirit and purpose of the United Nations than the terrorist attacks of Sept. 11."

Beyond the tens of thousands who gathered at the site, life did go on as normal in New York. Subways ran and were full; at Terry's, a coffee shop that was once frequented by office workers from the twin towers, people lined up to buy a hot cup, though they were silent as the radio broadcast the names of those who perished a year earlier.

"I'm going to work," Daniel Schwartz said. "I'll sell stocks today. I'll light a candle tonight. That's the best thing I can do for my country."

Julio Tello, a New Yorker who was escorting Canadian families of Sept. 11 victims, predicted the world will soon see another tower rising from ground zero.

"When my daughter told me that the towers had fallen, I started crying," he said. "But we will see another tower here. Maybe even taller than before."