Remembering the 9/11 terrorist attacks on New York that shook the world after 21 years

21 years have passed since the 9/11 attacks. The four al-Qaida assaults on the World Trade Centre and the Pentagon shocked the US to its core.

On September 11, 2001, terrorist attacks at the World Trade Center in New York City, the Pentagon building in Washington, D.C., and a plane crash near Shanksville, PA killed almost 3,000 people, including 400 police officers and firefighters.

Most of the hijackers were from Saudi Arabia. They came to the United States and went to flight schools without raising any red flags. 

The 9/11 attack on the World Trade Center was the foreign attack on American soil that killed the most people.

The New York City Fire Department lost 343 firefighters, almost half the number of on-duty deaths in the department's 100-year history.

After the September 11 attacks on the World Trade Center, it took 9 months to clean up the site, which had 1.8 million tonnes of wreckage.

Videos of the WTC attack were shown right away, but no videos of the Pentagon attack were shown to the public until 2006.

In 2006, construction workers found the remains of people in several places near where the Twin Towers used to stand. At the same time, the Environmental Protection Agency worked for years to clean toxic dust out of apartments downtown.

At the World Trade Center site, 18 people were found alive in the rubble.

People in and around the World Trade Center had an unusually high number of respiratory problems like asthma and lung inflammation during and after the attacks.

Lower Manhattan burned for 99 days following 9/11. Construction personnel could use excavators and other heavy equipment after the pile stabilised. The place remained hazardous. Fires underground lasted months. 

United Flight 93 passengers heard about past plane assaults and tried to reclaim control. As a result, the hijackers intentionally wrecked the jet in a Pennsylvania field.

In connection with the attacks, more than 1,100 people were arrested. About 780 people have been locked up at the American military prison at Guantánamo Bay, Cuba, since 2002.