Nearly 3,000 people died on the day of a series of coordinated attacks against the United States by terrorists who hijacked four passenger jets that crashed into the World Trade Center buildings in New York, the Pentagon and a field in rural Pennsylvania.

Smoke rises from the World Trade Center in the Manhattan borough of New York after the terror attack on Sept. 11, 2001.

World Trade Center buildings in New York

A U.S. Navy lieutenant dropped to one knee and placed flowers on a gravesite, while family, friends and coworkers of the 184 victims of the 11 September 2001 terrorist attack on the Pentagon, look on during a memorial service at the Arlington National Cemetery, 11 September 2003.

Smoke and flames in the Washington, DC, skyline in the aftermath of the terrorist attack on the Pentagon, 11 September 2001.

President George W. Bush greeted rescue workers, firefighters, and military personnel, 12 September 2001.

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