Americans commemorated the 25th anniversary of 9/11 on Friday, remembering the shock, the dead and the sweeping consequences of the al-Qaida attacks on symbols of US might and prosperity.

The milestone anniversary brought memorial rituals — wreath-laying, flag-flying, moments of silence, vigils and readings of victims’ names — and volunteer projects in tribute to a day that about half of US adults remember as the most historic event of their lifetime, according to a new poll.

On September 11, 2001, al-Qaida extremists hijacked four commercial jets and crashed them into New York’s World Trade Centre, the Pentagon and a field near Shanksville, Pennsylvania, killing nearly 3000 people.

Elsie Caldwell carried a photograph of her son Kenny Caldwell to the trade centre to hear his name and all the others read aloud Friday morning. She last spoke to him that morning a quarter-century ago.

“Mom, I just want to let you know that I love you,” Caldwell said he told her in a final phone call. His remains, like those of many other victims, have never been recovered.

Trump attends Pentagon observance

The attacks brought down the World Trade Centre’s twin towers — icons of US economic power, and among the tallest buildings on Earth — and blew a hole in the Pentagon, the US military’s fortress-like headquarters near Washington.

The fourth plane was headed for Washington, officials concluded, but the aircraft went down in Pennsylvania after passengers and crew members stormed the cockpit and fought the hijackers.

“September 11 reminded us of the terrible power of hate,” US President Donald Trump said on Friday at the Pentagon’s anniversary ceremony Friday.

“The 25 years since have shown us the even greater power of the American spirit to endure and prevail, and to win,” added the Republican, who was in his native New York on 9/11.

Former President George W. Bush, who was in office on 9/11, and ex-Presidents Bill Clinton, Barack Obama and Joe Biden and current Vice President JD Vance convened for the observance at the National September 11 Memorial in New York.

Other administration officials went to the Flight 93 National Memorial in Pennsylvania.

At ground zero, a new tribute to those who fell ill

For Angilic Casalduc, attending the New York commemoration “helps to show you’re not alone.” She lost her mother, Vivian Casalduc.

“There’s no timeline for grief, and unfortunately, no one can say how can you can grieve, but coming here once a year makes it feel just a little bit better,” she said.

Traditionally, there are no political speeches at the ground zero commemoration, where victims’ relatives read aloud the long list of names and added personal messages.

They thanked first responders and the military, invoked religious faith, appealed for national unity and touched on the US relationship with Saudi Arabia. The kingdom was the homeland of most of the hijackers but denied any involvement in the attacks.

Mostly, relatives spoke of, and to, loved ones — who some were too young to remember.

“You dreamed my whole life for me, and you only got eight months of it,” said Trisha Pakka, who lost her mother, Deepa Pakkala.

The ceremony has long been punctuated with moments of silence at key points in the attack timeline and this year organisers added another moment to honour people who were exposed to the clouds of toxic dust released by the twin towers’ fiery collapse and have since died of cancer and other illnesses. 

Questions remain about how many people developed health problems linked to the dust.

The impact of 9/11 endures

It’s a reminder of how the attacks’ long shadow has reached into many corners of life in the US and beyond.

The US-led global war on terrorism included invasions of Iraq and Afghanistan — the latter Washington’s longest war — and detentions and harsh interrogation of terror suspects in an international network of secret CIA prisons.

The US found and killed al-Qaida leader Osama bin Laden in Pakistan in 2011, but accused 9/11 mastermind Khalid Sheikh Mohammed still awaits a trial 23 years after his capture.

The attacks changed US air travel, led to the creation of the Department of Homeland Security, prompted new federal surveillance and intelligence-gathering powers and banking regulations and generated ongoing debate over the balance between security and freedom.

September 11 engendered a culture of individual vigilance summed up by the slogan ” if you see something, say something,” while a wave of patriotism propelled some Americans to join the military, fire departments, police forces or other public agencies.

Casey Kloepfer became a New York police officer this June. He was four when his father, Officer Ronald Kloepfer, was killed at the trade centre.

“It’s big footsteps to fill, but it’s definitely something that I take very seriously and want to continue to honour him and be the best police officer I can,” the 29-year-old, who wears his father’s badge number, said by phone this week.

New York’s mayor comes under scrutiny

Amid the post-9/11 calls to service and appeals for national unity, the attacks also fanned mistrust, prejudice and hate crimes directed at Muslims.

In the quarter-century since, Muslim Americans have played a growing role in public life from statehouses to Congress to New York City Hall, where Zohran Mamdani is the city’s first Muslim mayor. Yet he faced some criticism for attending the anniversary ceremony at ground zero.

Republican ex-Gov. George Pataki and 9/11 victims’ relatives cited, among other things, past remarks that some of Mamdani’s political associates have made about the attacks.

Former Mayor Rudy Giuliani, a Republican, also inveighed against Mamdani attending the remembrance, though the two shook hands there Friday.

Mamdani, a Democrat, said this week he loves the city and country and that he wanted the anniversary to focus on victims’ families, first responders and New Yorkers who helped one another after the attacks, which he called a “horrific act of terror.”

The 34-year-old mayor was an elementary school student in New York on 9/11.

Times Square billboards pause advertisements

Remembrances extended far from the attack sites, including beams of light projecting from New Hampshire’s Mount Washington, a stair climb at Mississippi State University’s football stadium and a ceremony at Honolulu’s 9/11 memorial.

September 11 isn’t a federal holiday, but Congress has designated it both Patriot Day and a National Day of Service and Remembrance.

“One appropriate way to remember is by serving,” says Jay Winuk, who lost his brother Glenn Winuk and then co-founded the volunteer organisation 9/11 Day with friend David Paine.

The group helps people find volunteer opportunities and this year arranged for dozens of Times Square billboards to pause their advertising at 9.11am on Friday.

Instead, they simply displayed the time.