Today marks the 16th anniversary of the Sept. 11, 2001 terrorist attacks. The coordinated plot began with the hijacking of four planes and ultimately ended with the deaths of nearly 3,000 people in New York, the Washington, D.C.-area and Pennsylvania. Below, a detailed look back at the events of that day, including video and photos. A word of warning: Much of the content may be disturbing, as anyone who lived through the day or witnessed its events already knows:
The airplanes hijacked on 9/11 begin taking off at 7:59 a.m.
The first to depart is American Airlines Flight 11, a Boeing 767 that leaves Boston's Logan International Airport for Los Angles with 92 people on board.
At 8:14 a.m., United Airlines Flight 175 -- a Boeing 767 with 65 passengers on board -- leaves Logan for Los Angeles.
American Airlines Flight 77 leaves Washington Dulles International Airport at 8:20 a.m. The plane, a Boeing 757 with 64 people on board, is headed for Los Angeles.
Finally, at 8:42 a.m., United Airlines Flight 93 departs from Newark International Airport. The Boeing 757, which carries 44 passengers, is bound for San Francisco.
The first crash occurs at 8:46 a.m. when Flight 11 slams into the north tower of New York's World Trade Center.
According to the 9/11 Commission Report, two flight attendants contact American Airlines as the plane is being hijacked to provide details of the emergency. They report the use of Mace or a similar spray, several stabbings and a bomb threat.
The last known communication from the plane comes when flight attendant Madeline "Amy" Sweeney, on the phone with American Flight Services manager Michael Woodward, says, "Oh my God we are way too low."
The second crash comes at 9:03 a.m., when Flight 175 flies into the south tower of the World Trade Center.
The last communication made with air traffic control comes at 8:42 a.m., but passengers provide details of the flight by contacting their families by phone.
Brian Sweeney calls his wife, Julie, to tell her the plane has been hijacked, and Peter Hansen tells his father, Lee, "I think they intend to go to Chicago or someplace and fly into a building."
President George W. Bush learns of the attacks at 9:05 a.m. while sitting in a second grade classroom at an elementary school in Sarasota, Fla. White House Chief of Staff Andrew Card informs him of the attacks, whispering into his ear during the students' reading lesson.
(AP Photo/Doug Mills)
Bush later shares his memories of that day with National Geographic. He explains that when he receives news of the first plane crash at 8:50 a.m. -- just before entering the classroom -- he believes it is "a light aircraft," and his reaction is "man, the weather was bad or something extraordinary happened to the pilot."
It isn't until Card informs him of the second plane that Bush understands America is under attack.
In an address from Emma Booker Elementary School in Sarasota, Fla., Bush calls the attacks "a national tragedy" and "an apparent terrorist attack on our country."
"I have spoken to the vice president, to the governor of New York, to the director of the FBI, and have ordered that the full resources of the federal government go to help the victims and their families, and to conduct a full-scale investigation to hunt down and to find those folks who committed this act," Bush says.
"Terrorism against our nation will not stand."
At 9:36 a.m., Secret Service agents evacuate Vice President Dick Cheney and his aides from his office to the Presidential Emergency Operations Center, a Cold War-era bunker beneath the White House.
Flight 77 crashes into Pentagon.
(AP Photo/Heesoon Yim, File)
According to the 9/11 Commission Report, passenger Barbara Olson calls her husband Ted -- the solicitor general of the United States -- to inform him of the attacks. She reports that the flight has been taken over and that the aircraft is "flying low over houses."
A few minutes later, air traffic controllers at Dulles International Airport observe a plane on their radar traveling at "a high rate of speed." Officials from Ronald Reagan Washington National Airport warn the Secret Service of the aircraft shortly before Flight 77 hits the Pentagon.
Just minutes after Flight 77 crashes into the Pentagon, the White House and U.S. Capitol are evacuated.
After burning for 56 minutes, the south tower of the World Trade Center collapses at 9:59 a.m. The fall, which kills approximately 600 workers and first responders, lasts 10 seconds.
The fourth hijacked plane crashes at 10:03 in a field in Shanksville, Pa.
(AP Photo/Keith Srakocic)
The 9/11 Commission Report reports that several passengers make calls from the plane and receive word of the other hijackings. Upon hearing the news that major cities were being targeted, the passengers decide to fight back:
Five calls described the intent of passengers and surviving crew members to revolt against the hijackers. According to one call, they voted on whether to rush the terrorists in an attempt to retake the plane. They decided, and acted.
At 9:57, the passenger assault began. Several passengers had terminated phone calls with loved ones in order to join the revolt. One of the callers ended her message as follows:"Everyone's running up to first class. I've got to go. Bye."
According to the 9/11 Memorial, the hijackers deliberately crash in a field to prevent passengers from retaking the airplane. The crash site in Shanksville is approximately 20 minutes flying time from Washington, D.C.
After burning for 102 minutes, the north tower of New York's World Trade Center collapses, killing approximately 1,400 people.
New York City Mayor Rudy Giuliani orders an evacuation of lower Manhattan, alerting everyone south of Canal Street to leave.
After all American air space has been cleared, Bush addresses the nation from Barksdale Air Force Base in Louisiana, informing citizens that the U.S. military "at home and around the world is on high alert status."
"Make no mistake, the United States will hunt down and punish those responsible for these cowardly acts," Bush says.
Hours after the attacks that morning, the 47-story 7 World Trade Center building collapses from ancillary damage. No one is in the building at the time.
Bush gives his final address of the day from the White House.
From the Oval Office, the president informs Americans that he has implemented federal emergency response plans, noting emergency teams and the military are already at work:
Today, our fellow citizens, our way of life, our very freedom came under attack in a series of deliberate and deadly terrorist acts.
The victims were in airplanes or in their offices -- secretaries, businessmen and women, military and federal workers. Moms and dads. Friends and neighbors.
Thousands of lives were suddenly ended by evil, despicable acts of terror.
The pictures of airplanes flying into buildings, fires burning, huge structures collapsing, have filled us with disbelief, terrible sadness and a quiet, unyielding anger.
These acts of mass murder were intended to frighten our nation into chaos and retreat. But they have failed. Our country is strong. A great people has been moved to defend a great nation.
It was, we were soon told, "the day that changed everything", the 21st century's defining moment, the watershed by which we would forever divide world history: before, and after, 9/11.
Ten years on, much of that early reaction to the day America realised, as New York magazine put it on the fifth anniversary, that "there really are ideological-cum-religious zealots out there intent on slaughtering us in large numbers", now looks exaggerated – albeit understandably. 11 September 2001 didn't change the world for ever.
The world is, however, a different place. So the question is: which of the many changes are genuine consequences of 9/11? One way of answering might be to ask what the world would be like if 9/11 had not happened.
There are obvious objections to counterfactual history, as speculating "what if?" is known by historians, if only because, as any of them will tell you, causality isn't easy to establish with certainty even in conventional historical research. But it does throw up some neat ideas – not least that in the big scheme of things, 9/11, horrific and cataclysmic as it was, may not have changed much at all.
If the al-Qaida plotters had not pulled off 9/11, many security and foreign policy experts believe it would only have been a matter of time before they managed something else.
Alternatively, a steady accumulation of smaller attacks – an embassy in Africa here, a warship in the Red Sea there – may have provoked a large-scale US response.
So an attack on Afghanistan (with all its disastrous consequences for neighbouring Pakistan, and hence, arguably, for the choices made by the 7/7 London bombers) was more or less on the cards, with or without 9/11.
Crucially, Iraq too may well have come under attack regardless. "There's quite a strong argument," says Anatol Lieven of King's College London's department of war studies, "that the Bush administration would have tried to invade and occupy Iraq anyway.
"The question is, would they have got away with it? Would they have been able to win over the more moderate Republicans, get it through the Senate, rally support at the UN, convince Tony Blair?
"I think Iraq would certainly have been more difficult for the US without 9/11, because Bush explicitly made that Saddam-al-Qaida link. But I think it would have tried."
Assuming the neocons did carry the day, "much of what has happened since would obviously have happened anyway", Lieven points out. "The extreme anger of the Muslim world, the blow to US military prestige, the rise of Iran – all of that would have happened."
Robin Niblett, director of Chatham House, feels it is questionable whether the US hawks would have won the day on Iraq without the "extreme shock" of 9/11. But he notes that much else in the broader world picture would have happened regardless.
"Economic growth, continuing globalisation, the rise of a giant consumer class … the twin towers and al-Qaida barely even dented that," he says. "The debt crisis would have happened, too.
"The fact that America had a $700bn defence budget, was spending $200bn, $250bn a year in Iraq and Afghanistan, that was a massive additional drain. But the underlying economic and financial causes were unrelated. And the whole Arab spring really had nothing to do with 9/11.
"I'm struggling to think of a single thing that I wouldn't see today if the twin towers hadn't happened."
It was not 9/11 but the invasion of Iraq that set in motion the real changes: the "emboldened" state of Iran; the significant hardening and legitimising of anti-American attitudes in Turkey; the fact that the leaders of "rogue states" such as Venezuela or Iran could pull off the unlikely feat of "presenting themselves as much-maligned forces for stability".
And it was the war in Iraq, notes Toby Dodge, of the LSE and the International Institute for Strategic Studies, that imposed such serious and lasting strain on transatlantic relations, and on relations within Europe.
"If the transatlantic relationship was born in 1945, it died on 9/11. The fact [is] that Le Monde could say on its front page, 'We're all Americans now,' and that the US could then so completely squander that with bombastic, imperialist incompetence," he said.
Other major post-9/11 winners, says Lieven, include China, which avoided the consequences of "a very gung-ho, almost McCarthyite anti-Chinese agenda" when Bush came to power to "benefit enormously from the fact that the US was spending itself into the ground on military hardware that was never going to be a threat to China".
And if the Bush White House had not been occupied with Iraq, it might not have resisted attacking North Korea, Lieven speculates. "That would have led it into a confrontation with China."
In fact one of the greatest victims of the US response to 9/11, argues Dodge, was the country's own strategic focus, which "just got completely skewed". Pakistan was neglected. Israel was neglected ("The road to Tel Aviv and Ramallah ran through Baghdad").
And so too, adds Niblett, were Latin America ("Bush was the guy who was going to open up Mexico") and Asia.
"Everything became focused on this one thing," Niblett says. "The US simply withdrew from pretty much everything else. As a result, Washington was largely absent at a senior level from the rest of the world, at a time when the rest of the world was changing, and growing, very fast indeed. That's not made things easy for Obama."
The pendulum swings, though. Niblett explains: "The fact that 9/11 was such a massive attack, that it drew such a massive, big-stick response, and that America saw that response fail … The US was, after all, checked, even in some ways defeated in Iraq.
"Current US foreign policy under [Barack] Obama, altogether more nuanced, more restrained, is a product of that. There's an awareness that the big stick approach doesn't always work."
Which is probably, in the grand scheme of things, a good thing. Because as Lieven suggests, America under Bush was spoiling for a fight.
"It's worth examining the agenda with which Bush came to power and which he pursued in the first eight months," he says. "Anti-Russia, anti-China, anti-Iran, anti-North Korea … If a 'non-9/11' had made Iraq impossible, it's perfectly possible the US would have got into equally terrible trouble. Just in different places."