They played the bagpipes again and recited the names of the dead like poetry. Bells tolled, and requiems by President Obama and other dignitaries filled the amphitheater of ground zero on Sunday as America looked back upon a contagion of terrorism and war and renewed its vows of remembrance.

On the 10th anniversary of Sept. 11, 2001, as a resilient nation reflected on its losses, thousands of families gathered at the new World Trade Center rising in Lower Manhattan, at the Pentagon in Northern Virginia and on a field of wildflowers in Pennsylvania to commemorate nearly 3,000 relatives killed on that infamous morning when hijacked jetliners were turned into missiles and a new age of terrorism was born.

The day’s centerpiece unfolded at ground zero, where more than 10,000 members of the victims’ families, and a handful of dignitaries and their wives, gathered in a parklike setting of swamp white oaks and emerald lawns — a strangely futuristic plaza with precisely spaced trees rising from a five-acre granite floor, surrounded by a gouged wasteland of unfinished skyscrapers and silent construction cranes.

In that panorama of trade center resurrection, with the Lower Manhattan skyline in the background and the skirmishing harbor and the Statue of Liberty in the distance, the families choked back tears, sobbed and cast flowers into the spillways of sunken granite pools set in the footprints of the fallen towers, and crowded around the bronze parapets of the “voids” where the names of all the dead are etched.

Amid the sounds of cascading waterfalls, family members bent low over the parapets to touch or kiss the names, and to weep. Many made paper tracings of the names, or inserted flowers and American flags into the crevices, and the parapets were soon thick with the colors and with red and yellow roses.

“It was real inspirational to come here after all these years and finally see his name,” Dennis Baxter, 65, of King of Prussia, Pa., said of his brother, Jasper, who died in the south tower. “I touched it. I didn’t know what else to do. It was really moving.”

It seemed like only yesterday: the indelible images of the twin towers smoking and disintegrating, of people falling from the sky as if in a dream. Yet a decade had gone, and thousands more had died in the wars in Afghanistan and Iraq, America had endured economic hardships and natural disasters, had learned to live with terrorist threats and had at last killed Osama bin Laden.

For most Americans, the catastrophe of Sept. 11, though still vivid, has acquired the perspective of tragic history. But for the families and friends of those who died, the milestone anniversary meant only that the haunting memories of broken lives and shattered dreams had receded hardly at all.

“It’s still unbelievable — it still seems like a nightmare,” said Trisha Scudder of Paoli, Pa., whose brother, Christopher R. Clarke, a bond salesman, was killed at the trade center. At ground zero ceremonies, she found small comfort in his name etched on the rolls of the victims.

Sunday’s commemorations were the culmination of weeks of cultural and civic events that revisited 9/11 and its global consequences, a national outpouring of music, films, plays, visual arts, books, television documentaries and symposiums that reflected America’s rich diversity and grew into an avalanche of introspection and analyses unrivaled since the turn of the millennium.

In cities and towns across America, the anniversary was marked with solemn and patriotic ceremonies, religious rites, tributes to the dead and even a political hiatus, as major Republican presidential candidates stepped off the campaign trail.

Giant flags were unfurled at football and baseball games, and at the United States Open tennis tournament, a three-minute clip shown on a giant scoreboard had Spike Lee, Mary Carillo, John McEnroe and Pete Hamill speaking of New Yorkers’ resilience.

The attacks were recalled in concerts, vigils, public forums and millions of homes, where people watched televised memorial events and talked of the painful things they had witnessed.

Around the world, smaller commemorations were held in many capitals, with political and religious leaders voicing renewed commitments to democracy and the fight against terrorism. The global scope was a stark reminder that the victims of 9/11 came from more than 90 countries.

On a resplendent morning in New York, with cool breezes and a blue sky brush-stroked by clouds that thickened into an overcast as the day wore on, many houses of worship, at the city’s behest, tolled bells in an interfaith gesture of solidarity at 8:46 a.m., the time when the first plane struck the north tower.

In New Jersey, more than 700 of whose residents died on 9/11, nearly every town, it seemed, had someone to mourn. Churches held special services, American flags flew on countless homes, and ceremonies were conducted in communities across the state.

On an elaborately choreographed day, bells rang for silence six times during the morning: at 8:46 a.m., when American Airlines Flight 11 struck the north tower; at 9:03, when United Airlines Flight 175 hit the south tower; at 9:37, when American Airlines Flight 77 hit the Pentagon; at 9:59, when the south tower fell; at 10:03, when Flight 93 crashed in Pennsylvania; and at 10:28, when the north tower came down.

And in an emotional catharsis that continued for more than three hours, family members recited the names of the dead, this time including those killed in Virginia and Pennsylvania as well as in the attacks on the trade center in 1993 and 2001.

The names have become central to the ceremonies, read over the years by first responders, children, siblings, parents and others. This year any family member could participate, and many of the 3,000 children who lost a parent joined in.

The recitation of 2,983 names was no dry ritual. Indeed, it became an extraordinarily powerful drama, a kind of epic poem that forcefully and relentlessly conveyed vivid memories the dead, and touched upon the implications of children growing up without a parent, of the emptiness of a home without a companion, of years of shared dreams and poignant hopes destroyed.

Stepping to microphones in pairs, carrying flowers and photos of the dead or wearing T-shirts bearing their likenesses, many added personal messages, speaking intimately to their loved ones, saying, in effect, we love you, we miss you, and renewing pledges of fidelity, telling of the births of grandchildren or other family events.

Voices quavered and faltered, rang with force and hope.

And when it was over, the silence was profound. You could hear only the wind sighing off the Hudson.

There were no religious services or formal prayers, not even a representative clerical contingent. On an occasion deemed too solemn for speeches, dignitaries led by President Obama and former President George W. Bush turned to poems and passages of literature to address the nation and the families whose sacrifices, they acknowledged, could hardly be assuaged with words.

Quoting from the 46th Psalm, Mr. Obama intoned: “Come behold the works of the Lord, who’s made desolations in the earth. He makes wars to cease to the end of the earth; he breaks the bow, and cuts the spear in two; he burns the chariot in fire.”

Mr. Bush quoted an 1864 letter of Abraham Lincoln to a Massachusetts mother of two sons killed in the Civil War: “I feel how weak and fruitless must be any words of mine which should attempt to beguile you from the grief of a loss so overwhelming. But I cannot refrain from tendering to you the consolation that may be found in the thanks of the Republic they died to save.”

Other readings were given by former Govs. George E. Pataki of New York and Donald T. DiFrancesco of New Jersey and former Mayor Rudolph W. Giuliani, who were in office at the time of the attacks; by Govs. Andrew M. Cuomo of New York and Chris Christie of New Jersey; and by relatives of victims of the Sept. 11 attacks. Mayor Michael R. Bloomberg, who oversaw the arrangements, was master of ceremonies, and firefighters, police officers, first-responders and members of the armed forces served as honor guards.

Musical selections captured the solemnity — Yo-Yo Ma performing “Sarabande” from Bach’s First Suite for Cello Solo; James Taylor singing “Close Your Eyes”; the flautist Emi Ferguson performing “Amazing Grace”; and Paul Simon intoning “The Sounds of Silence.” The Brooklyn Youth Chorus sang the National Anthem and “I Will Remember You,” and 60 firefighters and police officers played the bagpipes.

The National September 11 Memorial Plaza was opened and dedicated on Sunday. It is to be opened to the public starting Monday, though reservations are backed up for months.

While it has become a national shrine, like Pearl Harbor or Gettysburg, ground zero is still a 16-acre construction site. One World Trade Center has 82 of 104 stories built, and 4 World Trade Center has 50 of 64 stories up. More towers, a transportation hub and the National September 11 Museum are in various stages of construction.

In a whirlwind day, Mr. Obama and the first lady, Michelle Obama, flew to Shanksville, Pa., and to the Pentagon to lay wreaths and exchange words and hugs with the families of Sept. 11 victims. In Pennsylvania, thousands met in a field of goldenrod and Queen Anne’s lace to honor the 40 passengers and crew members who are believed to have saved the White House or the Capitol from destruction by rising up against the hijackers. In the evening, after his appearance at the Pentagon, the president spoke at the Kennedy Center in Washington. The nation commemorated the day in myriad ways.

In Mississippi, the Rev. Jon Shonebarger, a chaplain at a prison near Natchez, chose the occasion to open a new church. Faith Independent Baptist Church was nothing fancy — just a hotel meeting room, coffee, muffins and a stack of Bibles. But a dozen people attended, and the pastor called it a new beginning.

At the Lincoln County Fair in Fayetteville, Tenn., besides mule races and carnival rides, crowds doffed cowboy hats and saluted as two girls rode horseback carrying the American and Tennessee flags in honor of the anniversary.

In Dallas, Christina Rancke, 21, a student at Southern Methodist University whose father, Alfred Todd Rancke, an investment banker, was killed in the south tower, attended church with Paige McInerney, a cousin who had been in the World Trade Center on Sept. 11 and escaped.

“There’s not a day that goes by that I don’t think about him,” Ms. Rancke said.

The commemorations were hardly free of controversy. In New York area firehouses and police stations, where the sense of loss ran deep for comrades lost on 9/11, anger over Mr. Bloomberg’s refusal to invite a large contingent of first responders was palpable. His decision to de-emphasize religion at the ground zero events generated more discreet criticism.

Even as the anniversary unfolded, a nation that had not experienced a major terrorist attack in a decade had the jitters. Intelligence officials in recent days had rushed to assess a tip suggesting that two or three operatives of Al Qaeda had slipped into the country to set off a car bomb in New York or Washington to disrupt the ceremonies. Security at the trade center and other sites was extraordinarily heavy.

Two scares on passenger planes prompted defense officials to scramble F-16 fighters, one aboard an American Airlines flight from Los Angeles to New York, and the other aboard a Frontier Airlines flight from San Diego to Detroit. Both planes landed safely, and in each case, officials said, passengers dawdling in restrooms had aroused the suspicions.

As peace prevailed, the ground zero proceedings closed in the early afternoon with trumpeters of the city and Port Authority police, the Fire Department and the military services playing taps, the hauntingly beautiful refrain that closes the military day.

And as the sun went down and a rising full moon cast a silvery darkness over the night city, two powerful searchlight beams shot skyward from near ground zero, creating likenesses of the fallen towers in a “Tribute in Light.” The ghostly illuminations, it was said, would be seen for 50 miles until fading away at dawn.