At 8:46 a.m., American Airlines Flight 11 speared into the 110-story north tower. At 9:03 a.m., United Airlines Flight 175, shown here, crashed into the 84th floor of the south tower. Both towers collapsed.
Hijacked planes also crashed into the Pentagon and in a Pennsylvania field. Nearly 3,000 people died in the 9/11 attacks, which led to the U.S. declaring a war on terror that continues to this day.
On Sept. 11, 2001, terrorists caught the U.S. by surprise when they hijacked four commercial airplanes and used them as weapons in a bold series of attacks aimed at American landmarks, including New York City's World Trade Center.
Spencer Platt / Getty Images
A fiery blasts rocks the World Trade Center towers after being hit by two planes. The stunning aerial assaults on the huge commercial complex where more than 40,000 people worked on an ordinary day were part of a coordinated attack aimed at the nation's financial heart. They destroyed one of America's most dramatic symbols of power and financial strength and left New York -- and the rest of the country -- reeling.
"I'm asking myself if it can happen in America," a stunned Sen. Charles Grassley, R-Iowa, said as he and other lawmakers evacuated the Capitol. "Obviously it can."
Alex Wong / Getty Images
Smoke billows from the Southwest E-ring of the Pentagon building Sept.11, 2001, in Arlington, Va., after it was hit by hijacked American Airlines Flight 77.
Paul J. Richards / AFP
President Bush is interrupted at 9:07 a.m. during a school visit in Sarasota, Fla., by Andrew Card, his chief of staff, and told that a second plane has hit the World Trade Center. Bush leaves the school session and sets off on a secretive hopscotch flight aboard Air Force One, stopping at an Air Force base in Louisiana and NORAD headquarters in Nebraska before returning to the White House in late afternoon. "Thousands of lives were suddenly ended by evil, despicable acts of terror," Bush tells the nation during a late-night television address.
Marty Lederhandler / AP
People in front of New York's St. Patrick's Cathedral react with horror as they look down Fifth Ave toward the burning World Trade Center.
Richard Drew / AP
A person jumps from the north tower of the World Trade Center as another clings to the outside, left center, where American Airlines Flight 11 ripped into the building, touching off an inferno that brought the tower down less than two hours later. "About five minutes before the tower fell, you could see people jumping from the upper floors. I watched six either fall or jump..." said Steve Johnson, then an msnbc.com producer who was standing about six blocks from the tower.
Ernesto Mora / AP
Two women hold each other as they watch the twin towers burn.
Amy Sancetta / AP
Smoke and debris fill the air as the south tower collapses at 9:59 a.m. "Clearly, not even the police and FBI who had flooded the area were worried about collapse," said George Hackett of Newsweek. "They wouldn't have been anywhere near to the buildings as they were. If the first building hadn't essentially fallen straight down, its crash could have killed hundreds standing, like me, a few blocks away."
Suzanne Plunkett / AP
Smoke and debris fill the streets as pedestrians run for cover after the collapse of the south tower. What started as a bright sunny day turned to darkness. "Suddenly the top of [the tower] just shattered into tens of thousands of pieces," said Steve Johnson, then a producer with msnbc.com. "You could see the whole thing just disappeared. Then the smoke came up. The cops started yelling, 'Get back! Run! Get Away!' I ran inside a hotel, and it went black outside because of the dust."
Stan Honda / AFP
A woman covered in dust takes refuge in an office building after the top of one of the towers collapsed. The woman was caught outside on the street as the cloud of smoke and dust enveloped the area.
Shannon Stapleton / Reuters
Rescue workers move the body of the Rev. Mychal Judge, 68, away from the base of the north tower. Judge, the New York Fire Department chaplain, died in the line of duty when struck by debris from the south tower while administering last rites to a firefighter.
Daniel Shanken / AP
People flee across the Brooklyn Bridge to escape the carnage in lower Manhattan.
Gene J. Puskar / AP
FBI investgators comb the crater left by the crash of United Airlines Flight 93, carrying 45 people, in Shanksville, Pa. The plane was flying from Newark, N.J., to San Francisco when it was hijacked by al-Qaida terrorists as part of the Sept. 11 attacks. Some passengers tried to overpower the hijackers and regain control of the aircraft, but It crashed into a field near Shanksville. All on board, including the four hijackers, were killed.
Kathy Willens / AP
A woman reacts to an explosion at the World Trade Center towers while observing from the Brooklyn Promenade.
Doug Kanter / AFP
A man standing in the rubble calls out asking if anyone needs help, after the collapse of the first World Trade Center tower. Firefighters and other rescuers worked around the clock, searching for survivors in what looked like a war zone.
Ben Margot / AP
Delayed Southwest Airlines flights are seen on a television monitor after the attacks, at the Oakland International Airport in California. All flights in the country regulated by the FAA were cancelled, stranding travelers nationwide.
Mario Tama / Getty Images
People walk in the street in the area where the World Trade Center buildings collapsed,
Matthew McDermott / Corbis Sygma
A firefighter takes a break from searching in the rubble of the World Trade Center.
Thomas E. Franklin / AP
Firefighters raise a U.S. flag at the devastated World Trade Center.
Tom Stoddart / Getty Images
New Yorkers stand motionless and silent aboard the first Staten Island ferry to approach Manhattan after the World Trade Center attack.