After 3,652 days, it was as if everything had changed and nothing had changed.

Americans observed the 10th anniversary of 9/11 at hundreds of memorials around the nation, including major new ones in New York and Pennsylvania that transformed the sites of terrorist attacks that killed nearly 3,000 into places of healing and remembrance.

Yet the memories that flooded back were as sad and angry as ever.

Again, the specter of terrorism was abroad. Again, relatives held photos of missing loved ones with whom they'd hoped to reconnect. Again, children spoke to parents they never knew, and parents mourned children they had to bury — if they had anything to bury.

Standing at the spot where hijacked airliners destroyed the nation's two then-biggest office towers, John Gill Jr. held up a photo of his son, 34-year-old New York firefighter Paul Gill, and spoke to him: "We never found you. We never recovered you. But we know where you are — with our Lord in heaven."

Nicholas Gorki, 9, spoke of his father, "who I never met because I was in my mom's belly." But he thanked him nonetheless: "I love you, Father. … I love you for loving the idea of having me."

They were two among the scores of parents, siblings, children, domestic partners and other loved ones who read the names of the lost in ceremonies at the National September 11 Memorial in New York and the Flight 93 National Memorial near Shanksville, Pa.

Outside Shanksville, where passengers helped bring down a hijacked airliner apparently bound for Washington, nearly 5,000 people listened as victims' name were read aloud by relatives while bells tolled.

"This is not an easy morning," said Gordon Felt, whose brother Edward Porter Felt died in the crash. "Sept. 12, we began healing. While we can never be healed, we can embrace the healing process."

More than 1,000 relatives of those who died at the Pentagon filed slowly into the National 9/11 Pentagon Memorial and sat quietly in rows of metal chairs, facing the 184 metal benches — one for each victim — that make up the memorial.

To their right, a huge flag was draped over the Pentagon wall, marking the section where American Flight 77 crashed.

At 9:37 a.m., the moment the plane struck the building, there was a moment of silence, followed by a haunting rendition of Amazing Grace by the Navy chorus. The U.S. Army Band played solemnly as 184 servicemembers laid wreaths at the memorial benches.

In his speech, Vice President Biden invoked a "9/11 generation of warriors."

"Never before in our history has America asked so much over such a sustained period of an all-volunteer force," he said. "…The 9/11 generation ranks among the greatest our nation has ever produced, and it was born — it was born — it was born right here on 9/11."

The day saw security tight even by the standards of Sept. 11, particularly in New York and Washington.

Last week, the federal government had warned those cities of a tip about a possible car-bomb plot. Police searched commercial vans and trucks at bridges and tunnels in New York, and streets near the Trade Center were blocked. To walk within blocks of the site, people had to go through checkpoints. At the ceremony, President Obama and former president George W. Bush stood behind bulletproof glass.

In New York, the memorial's theme is absence and remembrance. The design, which took a full decade to select and build, features two huge pools in the shape of the Trade Center towers, lined by waterfalls and descending into the site. Victims' names are etched in bronze around the edge of the pools.

The Flight 93 Memorial, still incomplete, features a memorial wall along the edge of the crash site engraved with the names of the flight's 40 crewmembers and passengers. A gate allows family members to visit the "sacred ground" of the crash site.

The memorials' opening brought a symbolic end to a decade-long debate over how to physically commemorate 9/11, and brought obvious comfort to many of the bereaved.

In New York, sisters Maureen Wheeler and Michelle Fallon filled bottles with water from the memorial pools when they found the name of their brother, David Ruddle — a carpenter who died in the south tower.

Fallon said the sisters put his name on their parents' headstone, but the memorial "is like a resting place for him."

"It's peaceful to know that he's remembered," Wheeler agreed. "It's like being with him again."

Hilde Eicher, came to hear — and see — the name of her grandson Brian Joseph Cachia, who began working for Cantor Fitzgerald on the 103rd floor of the north tower five weeks before the attacks. He'd just gotten engaged. Eicher and Brian's aunt, Pat Cachia, had come to the ceremony every year. But, Cachia said, "once the 10th year is over, they'll all be gone again."

As always, the reading of the names in New York received an emotional charge from the readers' personal comments.

His voice cracking, Jefferson Crowther read the name of "my coureagous son," Welles, who died after helping to lead other office workers to safety at the Trade Center. Jefferson called his son "the man in the red bandanna," which is how one witness described the then-anonymous Good Samaritan.

Welles, who always carried a red handkerchief, wore it over his face on 9/11 to help him breathe. On Sunday, his father had a bright red one sticking out of the breast pocket of his blue blazer.

Lauren Fazio, speaking of and to her late father, Ronald, said his survivors are teaching his grandchildren "to always hold the door for others, just as Grandpa did that day."

It was an expression with special significance. Fazio's family says that on 9/11, Ronald, who worked on the 99th floor of the south tower, stayed behind to hold the door for colleagues and co-workers, to ensure they exited safely.

According to the Fazio family, one employee said that Ronald and others did not leave the floor until they were sure it was empty. His remains were never found. In his memory, his family later founded "Hold the Door ," a non-profit organization.

There were lighter moments. Ailish Coughlin said to her late father, Martin, an Irish immigrant to New York City: "I hope you're rockin' and rollin' with Elvis." Rachel Connor read the name of her father, Robert Crawford, a New York firefighter for 32 years: "As you always said, Daddy, 'We got your back.'"

Those who survived the attack also measured the day's meaning. Christopher Quimby, who escaped from the 87th floor of the north tower, attended observances in Rhinebeck, N.Y. He clutched his ID from that day. He said he was thinking about those who did not escape, and of the changes over the past decade. "We are an open society and security is as it can be, but the price you pay for freedom is a certain degree of vulnerability," he said.

Because it was Sunday, millions gathered in churches to "remember, question, pray and hope … for a world where such indescribable acts are but painful memories." That was the observation of Timothy Burger, an Episcopal priest preaching in Glen Rock, N.J. — a town of 11,000 that lost 11 people on 9/11.

In many denominations, the Gospel reading was from Matthew, and it was a difficult one. The disciple Peter asks Jesus, "How many times must I forgive one who sins against me?"

Not seven times, Jesus tells him, but 77 — in the vernacular of the time, forever.

Contributing: Haya El Nasser in Shanksville, Pa.; Oren Dorell in Arlington, Va.; the Poughkeepsie (N.Y.) Journal; the Associated Press