The United States will hold a series of events on Friday to mark the 25th anniversary of the September 11, 2001, attacks, one of the deadliest terrorist attacks in modern history.
On September 11, 2001, 19 hijackers seized four passenger planes and used them to carry out coordinated attacks against targets in New York and Washington. The attacks killed nearly 3,000 people and had far-reaching consequences for global security and international politics.
Four passenger aircraft flying over the eastern United States were hijacked by teams of attackers on the same morning.
Two of the planes were flown into the Twin Towers of the World Trade Center in New York. The second aircraft struck the South Tower 17 minutes after the first plane hit the North Tower.
The impacts triggered massive fires and sent thick smoke across lower Manhattan. Both 110-storey towers collapsed within two hours, killing thousands of people inside and around the buildings.
A third plane was flown into the Pentagon, the headquarters of the US Department of Defense, near Washington, D.C.
The fourth aircraft, United Airlines Flight 93, crashed into a field near Shanksville, Pennsylvania, after passengers attempted to regain control of the plane from the hijackers.
A total of 2,977 people, excluding the 19 hijackers, were killed in the attacks.
- 246 passengers and crew members aboard the four planes died.
- 2,606 people were killed at or later died from injuries sustained at the World Trade Center.
- 125 people died at the Pentagon.
Victims came from 77 countries. New York City also lost 441 first responders, including firefighters, police officers and emergency personnel.
The youngest known victim was two-year-old Christine Lee Hanson, while the oldest was 82-year-old Robert Norton, both of whom were passengers on the hijacked aircraft.
An estimated 17,400 people were inside the Twin Towers when the attacks occurred. No one above the impact zone in the North Tower survived, while 18 people trapped above the impact zone in the South Tower managed to escape.
Thousands of people were injured during the attacks and many others later developed serious illnesses linked to exposure to dust and toxic materials released by the collapsing buildings.
The attacks were planned by Al-Qaeda, an Islamist militant organisation led at the time by Osama bin Laden.
The group blamed the United States and its allies for their policies and military involvement in the Muslim world.
Khalid Sheikh Mohammed is widely identified as the principal architect of the 9/11 plot. He helped develop the plan and recruit the hijackers, several of whom received flight training in the United States.
The 19 hijackers were divided into four teams. Fifteen were Saudi nationals, two were from the United Arab Emirates, one was Egyptian and one was Lebanese.
Less than a month after the attacks, then-President George W. Bush authorised a US-led military invasion of Afghanistan aimed at dismantling Al-Qaeda and removing the Taliban from power.
Osama bin Laden remained at large for nearly a decade before US forces located and killed him in Abbottabad, Pakistan, in 2011.
Khalid Sheikh Mohammed was arrested in Pakistan in 2003. He was subsequently held at secret CIA detention facilities before being transferred to the US detention facility at Guantanamo Bay, Cuba.
His legal proceedings have been delayed for years amid concerns over the treatment he received while in US custody and whether evidence obtained during that period can be used in court.
A proposed plea agreement involving Mohammed and two other defendants was abandoned in 2025 after objections from the US government. The trial is currently scheduled for June 2028.
The attacks led to major changes in aviation and national security policies worldwide.
In the United States, the Department of Homeland Security was established, while the Transportation Security Administration was created to strengthen security at airports and aboard passenger aircraft.
The attacks also triggered the US-led “war on terror” and contributed to prolonged military campaigns in Afghanistan and elsewhere.
The cleanup of Ground Zero, the site of the destroyed World Trade Center towers, took more than eight months.
Today, the site houses the 9/11 Memorial and Museum, alongside a rebuilt World Trade Center complex. One World Trade Center, also known as the Freedom Tower, rises 1,776 feet (541 metres) and is the centrepiece of the new complex.
The Pentagon was also rebuilt following the attack, with employees returning to their offices by August 2002.
