At New York's ground zero, Obama touched the names of the lost etched into bronze at a memorial pool created in the footprint of one of the downed World Trade Center towers.
In a field in rural Pennsylvania, he walked the marbled Wall of Names and placed a wreath memorializing the 40 people who crashed at Shanksville after fighting back against the hijackers and driving their plane into the ground.
At the Pentagon, too, the president placed a wreath at a memorial where each of 184 victims is remembered with a bench and small reflecting pool. A brass quartet played a soulful rendition of "Amazing Grace" as the president greeted visitors to the memorial.
This was not a day centered on presidential speechmaking.
Rather, Obama's principal role was simply to be there as the nation paused to remember the nearly 3,000 lives lost and ponder all that has transpired.
At a ceremony at ground zero, Obama read Psalm 46, which he chose because it speaks of perseverance through challenges.
"God is our refuge and strength," Obama intoned, "a very present help in trouble. Therefore, we will not fear."
On a sun-splashed New York morning, Obama and his wife, Michelle, first walked with former President George W. Bush and his wife, Laura, to the North Memorial Pool. All four touched the names etched in bronze and silently bowed their heads. They then turned to dispense greetings and hugs to family members of those who died.
This also was not a day for partisanship or rancor.
Bush gave Obama a quick nod of solidarity after the president's reading. It was the first time the two presidents had seen each other since their Rose Garden appearance after the Haiti earthquake in January 2010.
The presidents and their wives stood behind bulletproof glass during the ceremony, an indication of the tight security surrounding the day's events. In Washington, Obama's chief counterterrorism adviser convened a meeting in the Situation Room to review security precautions for the weekend.
Obama's stop in Shanksville drew spontaneous applause and chants of "USA" from those at the memorial site, where each of the 40 marble slabs is inscribed with the name of someone who died in the crash. Obama and his wife lingered at the site to pose for photos with visitors, greet children and share some quiet laughs.
"Thanks for getting bin Laden," one man called out.
The Obamas then walked to the boulder that marks the actual crash site and stood quietly together in a field of wildflowers for a time.
"I think it's just important that the president shows his support for the families that lost loved ones," said Jaleel Dyson, an 18-year-old from Washington who attends college in the area and came to pay tribute to the dead.
At the Pentagon, the Obamas took their time mingling with memorial visitors and family members of those who died, some of them wearing ribbons and T-shirts bearing the names and photos of their loved ones. For all the solemnity of the occasion, there were smiles and laughter in the crowd as well.
Obama, who was a state senator from Illinois when the hijackers struck in 2001, has called on Americans this weekend to remember and serve, and to come together toward a joint future.
"Ten years later, I'd say America came through this thing in a way that was consistent with our character," he told NBC News.
"We've made mistakes. Some things haven't happened as quickly as they needed to. But overall, we took the fight to al-Qaida, we preserved our values, we preserved our character."
In the broadcast interview, Obama recalled going home after the attacks and rocking his baby daughter, Sasha. "Our first reaction was, and continues to be, just heartbreak for the families involved. The other thing that we all remember is how America came together."
President Obama said Sunday that the decade since the Sept. 11 attacks shows that America does not give in to fear, and never succumbed to suspicion and mistrust.
"These past 10 years tell a story of resilience," the president declared at the end of a long day of memories and reflection that took him to all three sites where hijacked planes struck on that frightening day.
Speaking at a memorial concert at the Kennedy Center, the president spoke of remembering the past, and of honoring the sacrifices of those who died in the attacks and the two long wars they spawned. But he also looked to a future when 9/11 will be seen through the eyes of generations that never witnessed the attacks themselves, and instead learned of them through memorials.
To them, the president said, the legacy of 9/11 will be the soldiers who signed up to serve, the citizens who withstood fear, the workers who built new towers to replace the old, and the children who lived out their parents' dreams.
"They will remember that we have overcome slavery and civil war, bread lines and fascism, recession and riots, Communism and, yes, terrorism," Obama said.
"It will be said of us that we kept that faith; that we took a painful blow, and emerged stronger."