Near the piles of rubble that once were the twin 110-story World Trade Center towers a rabbi, an imam and a priest said prayers, as firefighters, rescue workers and city officials stood bare-headed in a 20-minute respite from the grim task of searching for remains.
At the White House, in London, at the Pentagon and in outer space the 3,435 dead from the attacks were remembered.
"Every one of the innocents who died on September the 11th was the most important person on Earth to somebody," said President Bush in an East Room ceremony.
Bush said, "The struggle of humanity against tyranny is the struggle of memory against forgetting" and while the war against tyranny will one day be over "our remembrances never will."
He said a memorial of stone and metal may be erected to remind those in the future, "But for those of us who lived through these events ... We will remember where we were and how we felt."
At that moment, on Sept. 11, four U.S. jetliners were hijacked shortly after beginning cross-country flights. Two for the aircraft were flown into the twin towers of the World Trade Center. Another crashed into the Pentagon outside Washington. The fourth plane crashed in western Pennsylvania as passengers tried to take control of the jet from the hijackers.
Investigators said a total of 19 men -- all with Middle Eastern names -- carried out the coordinated hijackings. Government officials later said Osama bin Laden, a suspected terrorist leader based in Afghanistan, was the mastermind behind the plot. On Oct. 7, the United States began military operations against the Taliban, the Afghan rulers who were harboring bin Laden and his al Qaida network.
In New York at Ground Zero in Lower Manhattan, Rabbi Joseph Potasnik, chaplain of the New York Fire Department, said, "The terrorists took down those structures but they will not take away this spirit."
Other offerings came from the Rev. James Loughran, director of the Commission on Ecumenical & Interreligious Affairs of the Archdiocese of New York and Imam Tariq Shahid, assistant to Imam Pasha, who said, "Oh, our Lord, pour out on us constancy, and make our footsteps firm, and grant us victory over those who reject faith."
New York City Mayor Rudolph Giuliani sat with Gov. George Pataki and other governmental officials on a podium that included poinsettias and a menorah in front of the 16-acre site where the World Trade Center once stood.
At the request of Bush, the national anthem was played simultaneously across the country and at embassies worldwide at 8:46 a.m. Jazz trumpeter Joey Morant played the "Star Spangled Banner" at Ground Zero.
Nearby the giant cranes used to clear steel girders and rubble from the site paused for the brief service.
"It only gets harder," said Edward LaMotte, 36, of Brooklyn, a heavy-machine operator, who has been working seven days a week at the disaster site.
"It's nice that people are taking time out of their days to say prayers for us," added ironworker Michael Raiola, 27, of Brooklyn.
Of the 3,435 who died in the attacks, 3,045 were killed in the twin towers attack.
As the ceremonies began in New York and Washington, dozens of NASA flight controllers keeping watch over the shuttle Endeavor and space station Alpha joined seven American astronauts and three Russian cosmonauts to mark the event, with the playing of the American and Russian national anthems.
Flight director Wayne Hale said, "In stark contrast to the international cooperation and unity in our efforts to take mankind literally to the stars, we're reminded of our loss and sorrow due to the acts of violence and terror in an unprecedented attack on freedom, democracy and civilization itself."
He noted that among those who died were 200 citizens from countries who are party to the International Space Station program -- Canada, Italy, France, Germany, Japan and Russia.
On board the space station are 6,000 small American flags that will be given to family members of the victims, plus mementoes from the Pentagon, Pennsylvania and New York. also aboard is an American flag rescued from the World Trade Center rubble.
"It has a few tears in it. You can still smell the ashes," said Endeavor commander Dom Gorie in a recorded message that was replayed Tuesday, "Just like our country was a little but bruised and battered and torn, with a little repair it's going to fly high and as beautiful as it ever did and that's just what our country is doing."
In several states ceremonies were also marking the hour.
Texas Gov. Rick Perry in the Senate chamber in Austin recognized the Texas Task Force One, which helped search for victims in the early days of the Trade Center recovery. He paid tribute to the victors and said "We also join together to tell the evil perpetrators of this act -- we will not forget, and we will not rest, until justice is done.
Similar sentiments came from Illinois Gov. George Ryan at a ceremony outside the State Capitol attended by National Guard troops, and police and firefighters from Springfield. Perry said in addition to marking a "terrible national tragedy" they were honoring "the men and women who are waging a war on terrorism halfway around the world."