On September 11, 2001, hijacked passenger airplanes destroyed the World Trade Center in New York City and damaged the Pentagon in Washington D.C. killing near 3,000 people.
On Friday, a memorial service at Ground Zero is held to mourn the victims of the attacks.
Following is a brief timeline of the events of the day, according to the National September 11 Memorial & Museum.
8:46 AM: Hijackers deliberately crash American Airlines Flight 11, carrying 87 passengers and crew, into floors 94-98 of the North Tower (1 WTC).
By 9:00 AM: The Fire Department of New York (FDNY), the New York Police Department (NYPD), and the Port Authority Police Department (PAPD) mobilize at their highest levels.
9:03 AM: Hijackers deliberately crash United Airlines Flight 175, carrying 60 passengers and crew, into floors 78-84 of the South Tower (2 WTC).
By 9:15 AM: New York City officials begin closing bridges and tunnels to all except emergency personnel and pedestrians.
9:25 AM: The Federal Aviation Administration (FAA) orders the first ever nationwide ground-stop, prohibiting the take-off of flights.
9:37 AM: Hijackers deliberately crash American Airlines Flight 77, carrying 59 passengers and crew, into the Pentagon, near Washington, D.C.
9:40 AM: The FAA orders all 4,546 planes in North American airspace to land at the nearest airport.
By 9:45 AM: The White House, the Empire State Building, the United Nations, Disney World and other major U.S. sites are evacuated.
9:59 AM: The South Tower (WTC 2) collapses.
10:03 AM: After learning of the other attacks, passengers on United Airlines Flight 93, which carries 40 passengers and crew, launch a counter-attack on hijackers aboard their plane to try to seize control of the aircraft. In response, the hijackers crash the plane into an empty field in Somerset County, Pennsylvania.
10:28 AM: The North Tower (WTC 1) collapses. All 16 acres of the WTC site are in ruins. A rescue and recovery effort begins immediately.
11:02 AM: NYC Mayor Rudolph W. Giuliani orders the evacuation of all of Lower Manhattan below Canal Street, including workers, residents, tourists, and school children.
5:20 PM: 7 WTC collapses.
8:30 PM: President George W. Bush addresses the nation.