But the evening observances were disrupted when the police took a man into custody after finding several unattended backpacks near the finish line. The bomb squad was on the rainy scene and detonated one of the backpacks, creating a contained explosion.
The backpack was under a makeshift bridge across Boylston Street at the finish line; the bridge was set up as a platform for photographers for Monday's marathon. The streets were cleared of pedestrians.
Earlier, one of the most emotional moments of the day came at the very beginning, when Jane Richard, 8, and her brother Henry, 12, helped lay a wreath for Martin, their brother, in front of the Forum restaurant, where one of the bombs had gone off. Jane, with her prosthetic leg visible below her dark skirt, briefly touched the wreath, and they stood quietly for a few moments before turning to their parents for hugs. At the tribute, Governor Patrick took note of the few degrees of separation among those at last year's race. He said that Martin had carried a Deval Patrick campaign sign when Martin was only 2. Mayor Martin J. Walsh, who also spoke at the tribute, had been the boy's Little League coach.
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"It felt like we knew everyone who was hurt, everyone who was suffering," Mr. Walsh said, reflecting a quirk about Boston — that everyone seems to know everyone else and if they did not know one another before the marathon, they did now. They have learned their back stories and followed their progress.
The sense of community was evident, too, in the crowds that gathered in the downpour for a flag-raising ceremony on Boylston Street at the site of the explosions. Many recognized Carlos Arredondo, the cowboy-hat-wearing bystander who became famous last year when he helped rescue Jeff Bauman, who lost both legs. But Kristen McKenzie, 34, a nurse at Brigham and Women's Hospital, even recognized someone in the crowd far more anonymous: a man who had stood guard at a makeshift memorial that sprang up after the bombings.
"He was guarding that, day in and day out, so it was nice to see him," she said.
Perhaps the most intense bond that has been forged is that among a completely random group of people who had little in common except their enthusiasm for cheering on runners and the grave injuries they endured.
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The survivors have helped one another recover, moving from hospitals to rehabilitation together, some of them forming deep friendships. More than 100 of them even went on a cruise together in December.
"To our fellow survivor community," said Patrick Downes, speaking from the podium at the tribute, "what would we do without each other?" Mr. Downes and his new wife, Jessica Kensky, both lost their left legs in the blast.
Mr. Downes paid homage to the "individual snapshots of grace" he witnessed, mentioning "a department store employee searching for clothing to accommodate medical devices" and couples, wed and unwed, who stayed by one another's sides throughout their agonies, "in sickness and in health," he said. "Never has that vow felt so tangible."
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And to those who continue to struggle, despair and face "heart-wrenching surgical decisions," Mr. Downes said, "don't forget for a second that we will be there for you in a moment's notice."
In that spirit, Thomas M. Menino, who was mayor during last year's marathon, made what he called a solemn promise. "When the lights dim, the cameras go away, know that our support and love will never waver," he said. "Whatever you have to do to recover and carry on, know the people of Boston are right there by your side."
Vice President Joseph R. Biden Jr., who spoke last at the tribute, leaned on the lectern and clasped his hands in front of him, saying it was an important day, not just for Boston but for the country because Boston had inspired everyone.
"People know all about you," he said. "They know who you are, they know your pride, they know your courage, they know your resolve." (He confessed in an aside that he was not a Boston Red Sox fan. To be one where he grew up, he said — which was in Delaware as a Phillies fan — would have meant trouble.)
In a rousing finish, Mr. Biden summoned an image of next Monday, when runners will again line up to start the marathon, now in its 118th year.
"You will send a resounding message around the world, not just to the rest of the world but to the terrorists, that we will never yield, we will never cower, America will never ever, ever stand down," he declared. "We are Boston! We are America! We respond, we endure, we overcome and we own the finish line!"