Tuesday, September 11, 2001, began as a bright, sunny day in both Washington D.C. and New York City. Students went to school, and office workers prepared for another normal workday.
Then slowly, the news of a terrorist attack at the World Trade Center and the Pentagon reached people in classrooms, offices and in households across the country.
The scene played itself out again and again on television, radio and the Internet. Millions of people sat glued to the coverage, trying to make sense of the events as they progressed. Here is some background on that fateful day.
At 8:45 a.m., American Airlines Flight 11 crashed into a tower of the World Trade Center. The flight, starting in Boston, had 92 passengers.
About 20 minutes later, a United Airlines flight with 65 passengers from Boston crashed into the other tower.
People in those towers began running toward the exits, trying to get to safety. Many inside did not know why they were being evacuated until they were outside and could see the damage done by the planes.
Meanwhile, there were still two other hijacked planes in the air moving toward their targets. An American Airlines plane carrying 64 people from Dulles International Airport outside of Washington D.C. slammed into the side of the Pentagon building in Arlington, Virginia at 9:40 a.m.
A fourth plane, a United Airlines flight with 45 passengers from Newark, NJ, crashed into the ground outside of Pittsburgh around 10:00 a.m. There have been reports that the plane was headed for the White House or the U.S. Capitol building.
Numerous rumors began flying through the media about other attacks, from a bomb at the State Department to and explosion at the White House, but all were untrue.
The FBI and other federal government agencies began investigating the crashes immediately. Since Tuesday, they have identified the 19 hijackers and where they trained to fly the large airplanes used as moving bombs.
The government has named Saudi Arabia-born Islamic fundamentalist Osama bin Laden as the prime suspect behind the attacks. Some of the men who hijacked the planes had connections to bin Laden's organization, although it will be hard to prove a direct connection.
Over 40 people have been arrested in connection with the attacks.
Almost 200 people died at the Pentagon. Many more people have injuries. In New York, over 5,000 people are missing and presumed dead.
All 266 people aboard the four airplanes died.
The World Trade Center was a complex of seven buildings designed to be the center of trade business for many international countries. Over 40,000 people worked in the two main buildings, the Twin Towers, which were destroyed during the attack.
Because of their height (nearly four football fields stacked end to end) and fame, the Twin Towers were also popular for tourists. On a typical workday, 150,000 people visited to see the view from the top of the 110 floors, as well as to visit the 70 stores and restaurants contained in the complex.
Building Seven, a building near the downed Twin Towers that housed the city's emergency response team among other things, collapsed as well. That building stood 47 stories tall.
The World Trade Center was attacked once before by terrorists in 1993. Six people were killed and more than 1,000 injured when a bomb in a van exploded in a parking garage under the Twin Towers. The person who thought up that attack was quoted as saying that he wanted to take down both buildings but didn't have enough money for explosives.
Eventually, the buildings were repaired and normal operations continued.
The Pentagon is the headquarters of the Department of Defense. It is one of the world's largest office buildings. Over 20,000 employees, both military and civilian, work there.
It has never been attacked directly by anyone since it was built during World War II. Before the terrorist attack, most people thought it was impossible to penetrate.
America on defense
Many said that the terrorist attack was similar to another attack on the United States by a foreign enemy, The Pearl Harbor attack.
Japanese bomber planes attacked Pearl Harbor in Hawaii on December 7, 1941, killing nearly 2,400 people and bringing American into World War II.
You have go to further back in U.S. history to find the most recent attack on the 48 mainland U.S. Back during the War of 1812, British forces burned the new capital at Washington D.C. They also attacked Baltimore, New Orleans and Detroit, which at the time was a military outpost.
There was a brief invasion by Mexican troops across the Rio Grande began the U.S. - Mexican War in 1846, but the remaining action in that conflict occurred in territory belonging to Mexico.
day of firsts
The government also closed all airports for the first time in history and ordered all planes in the air to land immediately. Any planes coming from other countries were forced to turn around.
Many government buildings, including the White House, Supreme Court were evacuated. The Capitol Building, where Congress works, was evacuated for the first time.
This is the first time a major attack was waged on the U.S. from an unknown source during a time of peace.
Like with the 1995 bombing in Oklahoma City done by Timothy McVeigh, there will likely be a long investigation by the federal government and answers to many of the questions people still have.
For more on this topic, the Online NewsHour is following stories on the investigation and the U.S. reaction.
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