Bonita Mentis set out to read victims’ names at the ground zero ceremony wearing a necklace with a photo of her slain sister, Shevonne Mentis, a 25-year-old Guyanese immigrant who worked for a financial firm.

“It’s been 21 years, but it’s not 21 years for us. It seems like just yesterday,” Mentis said. “The wounds are still fresh.”

“No matter how many years have passed, nobody can actually comprehend that what happened that very day,” she added.

Victims’ relatives and dignitaries also convened at the other two attack sites, the Pentagon and a field in Pennsylvania.

More than two decades later, Sept. 11 remains a point for reflection on the hijacked-plane attacks that killed nearly 3,000 people, reconfigured national security policy and spurred a U.S. “war on terror” worldwide. Sunday’s observances, which follow a fraught milestone anniversary last year, come little more than a month after a U.S. drone strike killed a key al Qaeda figure who helped plot the 9/11 attacks, Ayman al-Zawahiri.

Pierre Roldan, who lost his cousin Carlos Lillo, a paramedic, said “we had some form of justice” when a U.S. raid killed Osama bin Laden in 2011.

“Now that Al-Zawahiri is gone, at least we’re continuing to get that justice,” Roldan said.

The Sept. 11 attacks also stirred — for a time — a sense of national pride and unity for many, while subjecting Muslim Americans to years of suspicion and bigotry and engendering debate over the balance between safety and civil liberties. In ways both subtle and plain, the aftermath of 9/11 ripples through American politics and public life to this day.

But like some other victims’ relatives, Jay Saloman fears that Americans’ consciousness of 9/11 is receding.

“It was a terrorist attack against our country that day. And theoretically, everybody should remember it and, you know, take precautions and watch out,” said Saloman, who lost his brother.

Like a growing number of those who read names at ground zero, firefighter Jimmy Riches’ namesake nephew wasn’t born yet when his relative died. But the boy took the podium to honor him.

“You’re always in my heart. And I know you are watching over me,” he said after reading a portion of the victims’ names.

More than 70 of Sekou Siby’s co-workers perished at Windows on the World, the restaurant atop the trade center’s north tower. Siby had been scheduled to work that morning until another cook asked him to switch shifts.

The Ivorian immigrant wrestled with how to comprehend such horror in a country where he’d come looking for a better life. And he found it difficult to form friendships as close as those he’d had at Windows on the World. It was too painful, he’d learned, to become attached to people when “you have no control over what’s going to happen to them next.”

“Every 9/11 is a reminder of what I lost that I can never recover,” Siby said in the lead-up to the anniversary. He’s now president and CEO of ROC United, a restaurant workers’ advocacy group that evolved from a post-9/11 relief center.

On Sunday, President Biden laid a wreath at the Pentagon and delivered remarks paying tribute to those who were killed in the attacks, saying the time that has passed “is both a lifetime and no time at all.”

“Terror struck us on that brilliant blue morning. The air filled with smoke and then came the sirens and the stories, stories of those we lost, stories of incredible heroism from that terrible day. The American story itself changed that day,” he said. “But what we will not change, what we cannot change, never will, is the character of this nation that the terrorists thought they could wound.”

The president expressed gratitude to the civilians and service members who swiftly responded to the attack at the Pentagon and the Americans who joined the armed forces in the wake of Sept. 11, declaring, “we owe you.”

“Through all that has changed over the last 21 years, the enduring resolve of the American people to defend ourselves against those who seek us harm and deliver justice to those responsible to the attacks against our people has never once faltered,” he said.

Mr. Biden also spoke of the importance of American democracy, saying the American people have an obligation to defend and protect it. The president has sounded an alarm about what he believes are assaults on democracy by some within the Republican Party who refuse to acknowledge the results of the 2020 presidential election.

“The American democracy depends on the habits of the heart, on ‘we the people,'” he said. “It’s not enough to stand up for democracy once a year, or every now and then. It’s something we have to do every single day. So this is a day not only to remember, but a day of renewal and resolve for each and every American and our devotion to this country, to the principles it embodies, to our democracy.”

First lady Jill Biden was also scheduled to speak in Shanksville, Pennsylvania, where one of the hijacked planes went down after passengers and crew members tried to storm the cockpit as the hijackers headed for Washington. Al Qaeda conspirators had seized control of the jets to use them as passenger-filled missiles.

Vice President Kamala Harris and husband Doug Emhoff joined the observance at the National Sept. 11 Memorial in New York, but by tradition, no political figures speak. The observance centers instead on victims’ relatives reading aloud the names of the dead.

Nikita Shah headed there in a T-shirt that bore the de facto epigraph of the annual commemoration — “never forget” — and the name of her slain father, Jayesh Shah.

The family later moved to Houston but often returns to New York for the anniversary to be “around people who kind of experienced the same type of grief and the same feelings after 9/11,” said Shah. She was 10 when her father was killed.

Readers often add personal remarks that form an alloy of American sentiments about Sept. 11 — grief, anger, toughness, appreciation for first responders and the military, appeals to patriotism, hopes for peace, occasional political barbs, and a poignant accounting of the graduations, weddings, births and daily lives that victims have missed.

Some relatives also lament that a nation which came together — to some extent — after the attacks has since splintered apart. So much so that federal law enforcement and intelligence agencies, which were reshaped to focus on international terrorism after 9/11, now see the threat of domestic violent extremism as equally urgent.

“It took a tragedy to unite us. It should not take another tragedy to unite us again,” said Andrew Colabella, whose cousin, John DiGiovanni, died in the 1993 bombing World Trade Center bombing that presaged 9/11.

Beyond the attack sites, other communities around the country marked the day with candlelight vigils, interfaith services and other commemorations. Some Americans joined in volunteer projects on a day that is federally recognized as both Patriot Day and a National Day of Service and Remembrance.