The attacks killed 2,977 people, excluding the 19 hijackers, and transformed global security, foreign policy, aviation, intelligence gathering and domestic politics.

They also set in motion wars, surveillance programmes and political changes whose effects continue to be felt 25 years later.

For families who lost loved ones, however, the anniversary remains deeply personal.

Jenna Jacobs McPartland was nine months pregnant when she learnt that a plane had struck the North Tower of the World Trade Centre.

Her husband, Ariel Jacobs, was attending a conference at the Windows on the World restaurant at the top of the tower.

“I called his office to say, ‘Hey, turn on the TV. Do you guys know what’s going on?’ His assistant said, ‘Oh my God, Jenna, he’s there.’ The whole world disappeared, and there was this sort of hollow collapsing feeling,” she recalled.

Ariel never met his son Gabriel, who was born six days after the attacks.

Twenty-five years later, McPartland continues to live with the grief while remembering her husband through an annual gathering at the cemetery where some of his remains are buried.

“Ari was an incredibly joyful person who cherished his life. I made a conscious choice to honour him by living as joyfully as I can,” she said. “The grief finds a place to live in the heart, and you visit it.”

Photo: Facebook/@911memorial/Det. Greg Semendinger, NYC Police Aviation Unit

A morning that changed history

On September 10, 2001, the United States appeared to be at the height of its post-Cold War power.

The country had emerged victorious from the Cold War, enjoyed relative peace during the 1990s and had recorded four consecutive federal budget surpluses between fiscal years 1998 and 2001.

The following morning shattered that sense of security.

Nineteen al-Qaida hijackers seized four commercial aircraft. American Airlines Flight 11 and United Airlines Flight 175 were flown into the World Trade Centre towers in New York.

American Airlines Flight 77 struck the Pentagon in Arlington, Virginia, while United Airlines Flight 93 crashed into a field near Shanksville, Pennsylvania, after passengers fought back.

Nearly 3,000 people died.

The attacks were broadcast around the world, with images of the burning towers, people fleeing through the streets of Manhattan and firefighters climbing into the smoke becoming part of the collective memory of the 21st century.

Historian David Blight described 9/11 as an exceptionally visual tragedy because of the enormous volume of photographs and footage captured that day.

“It’s the most visual event in history – so photographed, so much footage, so many documentaries,” he said. “There is a sheer sense of unspeakable loss.”

Photo: Wikimedia Commons/US National Park Service

Warnings before the attacks

The attacks did not emerge without warning signs.

The 9/11 Commission documented a series of intelligence warnings about Osama bin Laden and al-Qaida before the attacks.

By the summer of 2001, it concluded, “the system was blinking red”.

On August 1, the FBI warned that an attack inside the United States could not be ruled out. Another intelligence warning on August 3 said the threat of an al-Qaida attack was likely to continue.

On August 6, then-President George W Bush received a briefing titled “Bin Ladin Determined to Strike in US”.

The plot had been developed over years.

The 9/11 Commission traced al-Qaida's campaign against the US through the 1993 World Trade Centre bombing, the 1998 US embassy attacks in Kenya and Tanzania and the 2000 bombing of the USS Cole.

Khalid Sheikh Mohammed, later identified as the principal architect of 9/11, had considered using aircraft as weapons and eventually managed the operation.

Photo: Wikimedia Commons/Flickr/Michael Foran

How the hijackers took control

The 19 hijackers came from different backgrounds, but the plot depended heavily on an al-Qaida network centred in Hamburg, Germany.

Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah became three of the pilot-hijackers, while Hani Hanjour was the fourth.

The remaining 15 were described as “muscle hijackers”. Their role was to overpower passengers and crew and help secure control of the aircraft.

Several travelled through the United Arab Emirates, where al-Qaida facilitators helped arrange tickets, hotels and travellers' cheques.

Fourteen of the 15 muscle hijackers had entered the US by the end of June 2001, most using tourist visas.

Some had also triggered airport security alerts before boarding their flights.

Mohamed Atta was flagged before travelling from Portland, Maine, to Boston.

Several Flight 11 hijackers were also flagged. At Washington Dulles International Airport, multiple Flight 77 hijackers triggered security alarms.

Despite the alerts, all of them boarded their aircraft.

Photo: Wikimedia Commons/Kenneth Gross

8:46 am: The first impact

American Airlines Flight 11 departed Boston at 7:59 am.

Around 8:14 am, the crew stopped communicating normally with air traffic controllers.

Flight attendants Betty Ong and Amy Sweeney contacted ground personnel.

They reported that passengers and crew had been attacked, the cockpit could not be accessed, and the attackers had used a substance resembling mace or pepper spray.

The hijackers also claimed to have a bomb.

One of the attackers accidentally transmitted the words, “Nobody move. Everything will be okay,” over an air-traffic-control frequency.

At 8:46 am, Flight 11 crashed into the North Tower.

The Boeing 767 carried a large quantity of jet fuel.

The impact damaged structural columns and fireproofing across several floors.

The National Institute of Standards and Technology later concluded that the resulting fires weakened the exposed steel and contributed to the tower's eventual collapse.

Photo: Wikimedia Commons/Flickr/YU-bin

The second tower and Flight 93

United Airlines Flight 93 left Newark at 8:42 am, more than 25 minutes behind schedule.

That delay would become significant.

Passengers had additional time to learn about the attacks on the World Trade Centre before their own aircraft was hijacked.

United Airlines Flight 175 struck the South Tower at 9:03 am, while television networks were already broadcasting the first tower burning.

Flight 93 was hijacked at approximately 9:28 am.

Passengers and crew soon learnt what had happened in New York through telephone calls to people on the ground.

At 9:57 am, passengers launched their counterattack.

The aircraft's cockpit voice recorder captured the struggle as the passengers attempted to breach the cockpit.

The hijacker-pilot, Ziad Jarrah, made violent manoeuvres in an attempt to stop them.

At 10:03 am, Flight 93 crashed near Shanksville.

The 9/11 Commission concluded that the intended target was probably the US Capitol or the White House.

The passengers' decision to fight back prevented the aircraft from reaching Washington.

Photo: Wikimedia Commons/US Federal Govt

The Pentagon attack

American Airlines Flight 77 was hijacked between 8:51 am and 8:54 am.

Its transponder was switched off, causing it to disappear from conventional radar.

Controllers later detected the aircraft on primary radar as it approached Washington.

At 9:37 am, Flight 77 crashed into the Pentagon at around 900 kmph.

All 64 people aboard the aircraft died, along with 125 people inside the Pentagon.

The US Department of Defence puts the total Pentagon death toll at 189.

Aerial view of the Pentagon Building during the 9/11 terrorist attacks. Photo: Wikimedia Commons/TSGT CEDRIC H. RUDISILL, USAF

Collapse of the twin towers

The South Tower collapsed at 9:59 am, less than an hour after being struck.

Firefighters and police officers who had climbed the building to rescue people were among those killed.

At 10:28 am, the North Tower collapsed.

NIST estimated that around 87 percent of the roughly 17,400 people believed to have been in the two towers evacuated successfully.

The destruction of the towers sent enormous clouds of dust and debris through Lower Manhattan, while thousands of people fled the area.

Mystery of Building 7

World Trade Centre 7 became one of the most persistent sources of conspiracy theories surrounding 9/11.

The 47-storey building was not hit directly by an aircraft, but it collapsed at about 5:20 pm.

NIST concluded that debris from the North Tower damaged the building and triggered fires on several floors.

Water supplies for its sprinkler system had also failed, allowing the fires to burn for hours.

According to NIST, heat caused steel floor beams and girders to expand, eventually contributing to the failure of a key structural column and triggering a progressive collapse.

The agency also investigated claims that explosives had brought down WTC 7 and reported finding no evidence of explosives or a missile strike involving the building or the Twin Towers.

Photo: Wikimedia Commons/US Library of Congress/NY District Attorney's Office

‘America is under attack’

President George W Bush was in Florida when the attacks began.

At 9:05 am, his chief of staff Andrew Card entered the classroom where Bush was sitting with children and whispered that a second aircraft had struck the World Trade Centre.

Card told him: “America is under attack.”

The moment was captured in a photograph that became one of the defining images of the day.

The initial response brought an extraordinary display of courage and solidarity.

Firefighters, police officers and other emergency workers entered collapsing and burning buildings.

People queued to donate blood, while communities across the country organised support for victims and their families.

International solidarity was also immediate.

Russia offered support, Iran held candlelight vigils, and NATO invoked Article 5 of the North Atlantic Treaty for the first and only time in its history.

The then-US President George W. Bush gathers information about the World Trade Centre attacks, September 11, 2001. Photo: Wikimedia Commons/Eric Draper

From unity to 'War on Terror'

The initial unity was followed by a sweeping military and political response.

The US invaded Afghanistan to dismantle al-Qaida and remove the Taliban government that had sheltered the group.

The conflict lasted 20 years before the Taliban returned to power.

The Bush administration subsequently invaded Iraq in 2003 based on claims that Saddam Hussein possessed weapons of mass destruction.

Those weapons were never found.

The broader “War on Terror” expanded into military interventions, intelligence operations, detention programmes and interrogation practices, including torture at CIA black sites.

Guantánamo Bay became one of the most visible symbols of the post-9/11 era.

Hundreds of detainees were held there over the years, while the Abu Ghraib scandal in Iraq exposed widespread abuse and humiliation of prisoners.

9/11 mastermind Osama bin Laden. Photo: Wikimedia Commons/Hamid Mir

Security state at home

The consequences were not limited to foreign policy.

Just 45 days after the attacks, the US enacted the Patriot Act, significantly expanding the powers available to law enforcement and intelligence agencies.

The legislation became part of a much broader expansion of surveillance and counterterrorism powers.

Jameel Jaffer, who later litigated national-security cases for the American Civil Liberties Union and is now executive director of the Knight First Amendment Institute at Columbia University, has argued that many authorities created after 9/11 remain in place.

“So much of what’s going on now is traceable to the institutions and authorities that were created after 9/11 and that the courts failed to limit,” he said.

The period also transformed airport security, intelligence coordination and emergency preparedness in the US and internationally.

Bin Laden hunted for a decade

Osama bin Laden remained at large for almost 10 years after the attacks.

US intelligence gradually mapped his network and identified a courier connected to him.

By 2010, investigators had traced the courier to a compound in Abbottabad, Pakistan.

On May 2, 2011, US special operations forces raided the compound and killed bin Laden.

The al-Qaida leader's death ended the manhunt but did not end the broader threat from jihadist organisations, which subsequently evolved and spread through different regions.

The compound in Pakistan's Abbottabad, where Osama bin Laden was eliminated in 2011. Photo: Wikimedia Commons/Flickr/Sajjad Ali Qureshi

A generation without a memory of 9/11

A significant demographic change has also emerged.

A large share of Americans are now too young to have personal memories of September 11, 2001.

For them, the attacks exist primarily through photographs, documentaries, museums, school lessons and the stories of parents and survivors.

The 9/11 Memorial and Museum in New York, memorials at the Pentagon and Shanksville, and annual ceremonies have become important parts of preserving that history.

The legacy also extends into public health.

Thousands of first responders, survivors and people who lived or worked around Lower Manhattan have suffered illnesses associated with exposure to toxic dust and debris.

New York City has released more than 170,000 pages of previously undisclosed records concerning post-9/11 air-quality concerns, adding another layer to the long-running public-health story.

Photo: Facebook/@911memorial

PM Modi remembers victims

Prime Minister Narendra Modi wrote on X that 25 years after the 9/11 attacks, the victims and their families remained in the world's memory.

“25 years on from the horrific 9/11 attacks, we remember and honour the victims and stand in solidarity with the families whose lives were forever changed,” Modi wrote.

“Terrorism has claimed countless lives around the world. As a victim of cross-border terrorism, India has been at the forefront of this fight for several decades,” he added.

Modi said the nature of the terrorist threat continued to evolve but stressed that India's opposition to terrorism remained firm.

“While the threat keeps evolving, our resolve and opposition to terrorism in all its forms and manifestations remain unwavering. We stand in solidarity with all efforts to combat this scourge,” he wrote.

He also shared glimpses of his 2014 visit to the 9/11 Memorial and Museum in New York.

Trump honours first responders

President Donald Trump is marking the anniversary at the Pentagon rather than Ground Zero in New York, while Vice President JD Vance is attending the New York commemoration.

Trump also participated earlier in the week in a White House event honouring 9/11 first responders and Gold Star families.

At the September 8 event on the White House Ellipse, Trump stood beside a 21-foot steel beam recovered from the South Tower and posthumously awarded the Presidential Medal of Freedom to Welles Crowther, the equities trader and volunteer firefighter known as the “Man in the Red Bandana” for helping people escape the burning tower.

US President Donald Trump and JD Vance at the 9/11 remembrance ceremony, September 11, 2024. Photo: Wikimedia Commons/Flickr/US DHS

Trump said the attacks demonstrated the courage of Americans who ran towards danger and pledged that the country would “Never Forget”.

He has also spoken this week about his own experiences in New York following the attacks, including a claim that firefighters helped move him away from an unstable building.

That account has attracted renewed scrutiny, with reports noting that his descriptions of his role in the recovery effort have been disputed.

World remembers 9/11

The anniversary is also being marked outside the United States.

NATO is holding a ceremony at its headquarters in Brussels, where the alliance's 9/11 and Article 5 Memorial will be the focus of a remembrance attended by representatives of member states and NATO's diplomatic and military communities.

A moment of silence is scheduled for 14:46 CEST, corresponding to the moment the first plane struck the North Tower 25 years ago.

Photo: Facebook/@911memorial

In Jerusalem, US Ambassador to Israel Mike Huckabee joined Israeli and American officials at a memorial ceremony held ahead of the anniversary.

The Jerusalem memorial is the only site outside the US displaying the names of all 2,977 people killed in the attacks and includes a piece of metal recovered from the World Trade Centre.

Across the US, ceremonies are taking place at Ground Zero, the Pentagon and the Flight 93 memorial in Pennsylvania, while museums and institutions are displaying artefacts connected to the attacks and their aftermath.

The anniversary is also prompting a wider examination of the security and geopolitical changes that followed 9/11.

The attacks led to the creation of the Department of Homeland Security, expanded surveillance and major changes in aviation security, while the wars in Afghanistan and Iraq reshaped US foreign policy for two decades.

25 years later

The September 11 attacks remain both a personal tragedy and a defining geopolitical event.

For families such as McPartland's, the anniversary continues to revolve around people whose lives ended that morning.

For governments, the attacks transformed national-security policies and military priorities.

For a generation born after 2001, 9/11 has become a historical event whose meaning is increasingly transmitted through memory, testimony and institutions.

Photo: Facebook/@911memorial

Twenty-five years later, the images remain familiar: four hijacked aircraft, two collapsing towers, smoke rising from the Pentagon, Flight 93 falling in Pennsylvania, emergency workers moving towards danger and families waiting for news that never came.

The scale of the attacks was measured in minutes, and their consequences have continued for a quarter of a century.