Jan. 15, 1943: Construction of the Petagon is completed.
1970: One World Trade Center, the north tower, is built.
1972: Construction is completed on the second tower.
1988: Saudi exile and millionair Osama bin Laden establishes al Qaeda to support Islamic resistance in Afghanistan.
Feb. 26, 1993: A 1,000-lb. bomb in a Ryder van explodes in the garage of the World Trade Center, killing six people and injuring 1, 042.
Jan. 7, 1998: A US judge sentences Ramzi Yousef, a ontime follower of bin Laden, to life in prison without parole for masterminding the 1993 bombing.
Feb. 22, 1998: Bin Laden issues an edict calling for attacks on all Americans, including civilians.
1998-99: A grand jury indicts bin Laden in the 1998 bombings of US embassies in Africa, which killed 224 people.
July 2000: Two men named Mohamed Atta and Marwa Alshehhi reportedly begin flight school at Huffman Aviation in Venice, Fla. At least seven of the hijackers are believed to have been trained pilots.
May 29, 2001: Four followers of bin Laden are found guilty in a US district court of conspiring to kill Americans around the world, including those in the 1998 embassy bombings.
7:59 a.m. EDT: American Airlines Flight 11, carrying 92 people, leaves Boston's Logan International Airport for Los Angeles.
8:01 a.m.: United Airlines Flight 93, carrying 45 people, leaves Newark, N.J., International Airport for San Francisco.
8:10 a.m.: American Airlines Flight 77, carrying 64 people, takes off from Washington's Dulles Airport for Los Angeles.
8:14 a.m.: United Airlines Flight 175, carrying 65 people, leaves Boston for Los Angeles.
8:28 a.m.: American flight 11 veers south toward New York. The air-traffic controller handling the plane in Nashua, N.H., hears a conversation in the cockpit and realizes a hijacking is under way.
8:48 a.m.: American flight 11 crashes into the north tower of the World Trade Center.
9 a.m.: President Bush arrives at a Sarasota, Fla., school to give a speech, when he is informed a plane hs crashed into the World Trade Center.
9:03 a.m.: United Flight 175 crashes into the south tower of the World Trade Center.
9:05 a.m.: Bush is visiting a class when White House Chief of Staff Andrew Card whispers to him that a second plane has struck the World Trade Center.
9:31 a.m.: Bush calls the crashes an "apparent terrorist attack on our country."
9:43 a.m.: American Flight 77 crashes into the Pentagon. Trading on Wall Street is called off.
9:48 a.m.: The Capitol and West Wing of the White House are evacuated.
9:49 a.m.: The Federal Aviation Administration bars aircraft takeoffs across the country. International flights in progress are told to land in Canada.
9:50 a.m.: Two World Trade Center - the north tower - collapses.
9:58 a.m.: Emergency dispatcher in Pennsylvania receives a call from a passenger on United Flight 93 about hijacking. "We are being hijacked! We are being hijacked!"
10:10 a.m.: United Flight 93 crashes 80 miles southeast of Pittsburgh.
10:29 a.m.: One World Trade Center - the north tower - collapses.
10-11:30 a.m.: Government buildings around the US are evacuated. The UN closes down. All US financial markets are closed. New York Mayor Rudolph Giuliani calls for evacuation of lower Manhattan.
11:40 a.m.: Bush arrives at Barksdale Air Force Base, Louisiana, from Florida.
1:04 p.m.: Bush says US armed forces are on maximum alert and vows to "hunt down and punish" those responsible. "We will make no distinction between terrorists who committed these acts and those who harbor them," he says.
2:51 p.m.: The Navy dispatches missile destroyers and other equipment to New York and Washington.
3:07 p.m.: Bush arrives at US Strategic Command at Offutt Air Force Base in Nebraska.
4:36 p.m.: Bush departs for Wasington. En route, he phones Laura Bush, the first lady, and says, "I'm coming home, see you at the White House."
5:25 p.m.: Seven World Trade Center collapses.
7 p.m.: Bush arrives in Washington.
About 7:30 p.m.: Congress declares its bipartisan support for Bush in finding and punishing those responsible for the attacks. Members conclude by singing "God Bless America" on the steps of the Capitol.
About 8:30 p.m.: Bush addresses the nation.
For the first time in its history : NATO members involke Article 5 of the Washington Treaty, declaring an attack against one to be an attack against all.
Three survivors are pulled from the rubble at the World Trade Center, raising the total found to five.
Afternoon: Bush visits military rescue workers at the Pentagon.
Evening: Congress holds prayer vigil.
Officials confirm that a car believed to belong to hijackers was confiscated in Boston and that it contained an Arabic-language flight manual. Investigators also raid two area hotels believed to be used by the hijackers.
Queen Elizabeth II orders "The Star-Spangled Banner" played at the changing of the guard at Buckingham Palace in London.
About 1:45 p.m.: Secretary of State Colin Powell names Osama bin Laden a suspect in Tuesday's terrorist attacks.
New York Mayor Giuliani announces that 4,763 people are missing in New York.
Pentagon announces that 188 people are missing or dead in the attack on Washington.
Bomb threats are reported around Manhattan. No bombs are found.
At least 18 hijackers commandeered the four planes, Attorney General John Ashcroft says.
About 4:20 p.m.: Workers recover flight-data recorder from United Flight 93 at the Pennsylvania crash site.
Airports reopen across the country, but commercial flights remain limited. Boston's Logan Airport and Washington's Reagan National remain closed by order of FAA.
5:45 p.m.: FAA announces it has shut down LaGuardia, Kennedy, and Newark Airports due to "FBI activity."
About 4 a.m.: The cockpit voice recorder and flight-data recorder are recovered from the Pentagon crash site, a spokesman says.
6 a.m. (10:00 a.m. GMT): Europe observes three minutes of silence in a day of mourning. Among the gestures of support: Some 200,000 people gather at the Brandenberg Gate in Berlin, and many businesses in Ireland close for the day. In England, newspapers print US flags for people to display.
Declaring Friday a national day of prayer and remembrance, Bush attends a service at the National Cathedral in Washington.
Justic Department revises number of hijackers to 19, and releases names of suspects, including Atta and Alshehhi.
2 p.m.: Bush announces he has declared a state of emergency and signed an order calling up 50,000 reservists for "homeland defense."
About 2 p.m.: Both the House and Senate approve $40 billion to help the victims and hunt down perpetrators. Later, Congress grants Bush authority to take military action.
About 3 p.m.: Bush arrives in New York and visits rescue efforts a the World Trade Center.
About 8 p.m.: Justice Department announces it has made its first arrest in the investigation. The warrant was issued for a material witness. FBI Director Robert Mueller also says 30 subpoenas have been issued.
8:25 p.m.: Workers at the Pennsylvania crash site locate cockpit recorder for United Fight 93.
5 a.m.: Boston's Logan Airport reopens. Washington National remains the only airport still shut down.
About 9:50 a.m.: Bush names bin Laden the "prime suspect" and tells the military to get ready.
Giuliani announces that workers have cleared more than 22,000 tons of rubble, out of the 450,000 tons total. The number missing in New York totals 4,972.
Pentagon activates Operation Noble Eagle.
Pakistan offers support to the US. Among US reequests, the right for US jets to fly over its airspace.
The FBI has 4,000 agents tracking down 40,000 leads in the attacks. They have arrested two peole in the New York area.
Sources: The Associated Press, Reuters, "Frontline" and FEMA