On that Tuesday in September 2001, 19 members of the Islamic extremist group al-Qaeda coordinated attacks using hijacked U.S. airliners.
The group of terrorists deliberately crashed two airplanes into the North and South Towers of the World Trade Center and a third plane into the Pentagon.
The fourth flight crash-landed in a Shanksville, Pennsylvania, field. It is believed that the hijackers crashed the plane in that location, rather than their unknown target, after the passengers and crew attempted to retake control of the flight deck.
Nearly 3,000 people were killed that day, a day that will never be forgotten in the hearts of the American people.
9/11/01 TIMELINE: How the September 11, 2001 attacks unfolded
Here's a look back at the September 11 attacks by the numbers.
- 2,977 people were killed (and countless more suffered serious injuries and long-term health issues)
- 2,753 died at the World Trade Center site
- 343 of them were New York City firefighters
- 23 were NYPD officers
- 37 were police officers from the Port Authority of New York and New Jersey
- 184 people were killed when American Airlines Flight 77 crashed into the Pentagon
- 40 were killed on United Airlines Flight 93 that crashed near Shanksville, Pennsylvania
- Countless victims and first responders are still dying due to 9/11-related illnesses
- The victims ranged in age from two to 85 years. Approximately 75-80% of the victims were men.
- As of 2021, 1,647 (60%) of 2,753 WTC victims' remains have been positively identified, according to the medical examiner's office. Two new identifications of victims -- Dorothy Morgan and a man whose name is being withheld at the request of his family -- were announced Sept. 7, 2021.
- 19 men hijacked four planes
- The estimated economic loss during the first two to four weeks after the World Trade Center towers collapsed was $123 billion.
- It took 3.1 million hours of labor to clean up 1.8 million tons of debris at Ground Zero. Cleanup officially ended May 30, 2002.
PHOTOS: 9/11 attacks on the World Trade Center in New York City
The Associated Press and CNN Wire contributed to this report.