President Barack Obama read Psalm 46 from the Bible as he stood before the white oak trees of the new Sept. 11 memorial. The president read the psalm at 8:46 a.m., when the first jetliner slammed into the World Trade Center's north tower a decade ago.
"God is our refuge and strength," the psalm said. "He dwells in his city, does marvelous things and says, be still and know that I am God."
Former President George W. Bush quoted a letter from President Abraham Lincoln to a mother who was believed to have lost five sons in battle during the Civil War.
"I pray that our heavenly father may assuage the anguish of your bereavement," Bush said.
The New York ceremony was the centerpiece of a day of remembrance across the country. It was a chance to reflect on a decade that changed American life, including two wars and the overhaul of everyday security at airports and in big cities.
In a ceremony at the Pentagon, Defense Secretary Leon Panetta observed a moment of silence at 9:37 a.m., marking the time a jet struck the center of the nation's military. He paid tribute to 6,200 members of the U.S. military who have died in the Iraq and Afghan wars.
In Shanksville, Pa., a choir sang at the Flight 93 National Memorial, and a crowd of 5,000 listened to a reading of the names of 40 passengers and crew killed aboard the plane.
Earlier in New York, Obama and Bush bowed their heads at the World Trade Center site and ran their hands over the bronze-etched names of the victims of the attack.
The president and former president were joined by their wives as they walked up to one of the two reflecting pools built over the towers' footprints. The fountains, which represent falling tears, are a part of a Sept. 11 memorial for relatives of the victims.
Families found the names of their loved ones and ran their hands over the smooth bronze. Some even took out pencils and made impressions of the engraved names onto white papers, trying to take home part of what they lost.
Tom Frost of Orange County was at the site to remember his daughter Lisa, who was on Flight 175 when it crashed into the South Tower.
"When I saw Lisa's name on the wall, I had a lot of tears. It broke me in half," he said. "I was filled with a sense of pride that Lisa is one of the heroes of 9/11. She was on the front lines on the war on terrorism. She saw the terrorists face to face."
Obama and Bush later embraced family members and talked to dignitaries, including New York Mayor Michael Bloomberg, former Mayor Rudolph Giuliani and the governors of New York and New Jersey.
Victims' family members read the names of the 2,983 who died in the attacks - 2,977 killed in New York, Washington and Pennsylvania on Sept. 11, 2001, and six killed in the first terror attack on the trade center, a truck bomb in 1993. The ceremony lasted more than five hours, ending with the playing of taps.
The sky was clear blue over New York City with scattered white clouds and a light breeze - not unlike the Tuesday morning 10 years ago.
The site looked utterly different than it had for any other Sept. 11 anniversary. Along with the names in bronze, there were two manmade waterfalls directly on the footprints of the towers, surrounded by dozens of white oak trees.
The anniversary arrived with security officials in New York and Washington on alert. The lectern at the trade center site had bulletproof glass. Ahead of the anniversary, the federal government had warned local authorities of a tip about a possible car-bomb plot.
The anniversary revived memories of a September morning when terrorists crashed hijacked planes into the World Trade Center and the Pentagon, and a fourth plane crashed into a field in rural western Pennsylvania. It revived memories of heroism and Samaritans and unthinkable fear and the many killed at the hands of a global terror network led by Osama bin Laden, who is now dead.
People across America planned to gather to pray at cathedrals in their greatest cities and to lay roses before fire stations in their smallest towns. Around the world, many others will do something similar because so much changed for them on that day, too.
On Saturday, more than 4,000 people gathered in rural western Pennsylvania to tell the story all over again.
At the dedication of the Flight 93 National Memorial near the town of Shanksville, Bush and former President Bill Clinton and Vice President Joe Biden joined the families of the 40 passengers and crew aboard the jet who fought back against their hijackers.
The Pennsylvania memorial park is years from completion, but the dedication and a service to mark the 10th anniversary of the attacks are critical milestones.
World pays tribute on Sept. 11
As the anniversary arrived around the world, people paid tribute in formal ceremonies and quiet moments.
In Japan, they gathered Sunday to lay flowers before a glass case containing a small section of trade center steel, and remembered 23 employees of Fuji Bank who never made it out of the towers.
A village in the Philippines offered roses, balloons and prayers for an American victim whose widower built 50 brightly colored homes there, fulfilling his late wife's wish to help the Filipino poor.
In Malaysia, Pathmawathy Navaratnam woke up and, as she has done every morning for 10 years, wished "good morning" to her son, a 23-year-old financial analyst who was killed in New York.
"He is my sunshine. He has lived life to the fullest, but I can't accept that he is not here anymore," said Navaratnam. "I am still living, but I am dead inside."
The Associated Press contributed to this report.