World Trade Center, 2001 Terrorist Attack

World Trade Center, 2001 Terrorist Attack


At 8:46 a.m. on September 11, 2001, American Airlines Flight 11, hijacked from Boston's Logan Airport with 92 people on board, crashed into the upper floors of the World Trade Center north tower in lower Manhattan, New York. Seventeen minutes later, United Airlines Flight 175, also hijacked from Logan and with 65 people on board, crashed into the south tower. By this time, virtually the entire nation had tuned in to witness the after-effects on television of what at first seemed a terrible accident, but was quickly revealed as a terrorist attack. Over the course of the next 85 minutes, the south tower collapsed, followed by the collapse of the north tower. The incident, in which nearly 3,000 people died, ranks as by far the worst case of mass murder in U.S. history, the worst building disaster in human history, and the largest terrorist incident in the history of the western world.

The Towers and their Environment

Designed by architect Minoru Yamasaki—who, ironically, had a fear of heights—and engineered by Leslie Robertson and John Skilling, the 110-story towers soared 1,360 feet (415 m) above an open plaza, which made them the world's tallest buildings at the time of their completion in 1973. Whereas the Empire State Building and other older skyscrapers drew support from an interior grid of steel girders, support for the trade towers came from the exterior and the inner core. Horizontal floor trusses joined the perimeter support structure to the central area, which the engineers envisioned as a great "tube" running through the building and containing not only its support structure, but also its utilities such as elevators. This design had two advantages; it made the buildings extremely stable—not prone to swaying in high winds as the Empire State did—and it left much of the interior available as rentable space.

To support such a structure required a strong foundation, and in this regard, the location in lower Manhattan was not a promising one. Bedrock lay between 55 and 80 feet (17–24 m) below street level, and to get to it, construction crews had to deal with another engineering challenge: flooding from the nearby Hudson River. In order to dig without flooding the site, they dug narrow trenches to the bedrock, and as they went, they pumped in a slurry of water and bentonite, a type of clay that expanded to prevent groundwater from flowing in. The slurry trench method made it possible to build a watertight framework for the excavation of the foundation structure, nicknamed "the bathtub."

Excavation began in 1966, and yielded such a quantity of fill that it was used to reclaim 28 acres (11.3 hectares) from the Hudson to form Battery Park City. In addition to supports, in the area underneath the buildings would be seven stories of parking decks, stores, and subway lines. The erection of the buildings themselves, which took more than five years, was a massive feat of both construction and logistics, involving 200,000 tons (181,437) of steel, each major piece of which was marked with an identification number. Over the years of building, many businesses moved in long before the towers were officially completed.

28 years in the towers' lives. On April 4, 1973, the World Trade Center officially opened for business. Though the towers were by far the most notable aspect of the project, they were just two of seven buildings in the entire complex. Built at a cost of $1 billion, the towers functioned as virtual cities unto themselves, with some 500 businesses, including banks and their offices, law firms, brokerage houses, television stations, charitable organizations, airlines, and government offices. Supporting these functions and the 50,000 employees who filled them were numerous restaurants—most notable of which was "Windows on the World" at the top of the North Tower—as well as other services, including nine chapels of different faiths.

By the 1980s, New Yorkers had become accustomed to the trade towers, which punctuated the skyline as the ultimate symbol of American commerce. Then, in February 1993, just months before the towers turned 20, the towers became the target for a bombing by Islamist terrorists operating a van filled with explosives. In this, the first terrorist attack, six people were killed, but the structural integrity of the towers themselves was not threatened.

September 11 and Its Aftermath

Because of the 1993 attack, many Americans who witnessed the events of September 11, 2001, quickly realized that the buildings had once again become the target for terrorists. When Flight 11 crashed into the North Tower of the World Trade Center at 8:46 a.m., smoke and flames began to gush from the upper stories, and workers began to evacuate the lower floors. Some, however, chose to remain at their desks. For workers on the floors above the impact area, there was no choice but to remain in place.

For 17 minutes, it was possible to assume that what had happened to the North Tower was an accident; then, Flight 175 smashed into the South Tower. Once again, smoke and flames erupted from the heights of the building, and tenants down below began a slow, but steady evacuation while others—many with no choice—stayed where they were.

By 9:59 a.m., millions of Americans had turned on their television sets to watch live reports from the site. Thus, there was a vast audience to experience what happened next, an event that would be etched upon the consciousness of an entire nation. With little warning, the South Tower, succumbing to the stress caused by the fire, began to crash from the top down, creating a vast cloud of dust and ash above and filling the streets below with noise and heat and terror.

By 10:28 a.m., the North Tower began to implode, once again crashing downward from the top, and the area around what had once been the World Trade Center became smoke, ash, and dust. The other five buildings in the former World Trade Center complex, including the Marriott Hotel, the Commodities Exchange, Dean Witter, the U.S. Customs House, and 7 World Trade Center, were destroyed as well. The last of these caught fire, and collapsed that night.

Rescue, cleanup, and the death toll. In the next days and weeks, some 1,500 firemen, search and rescue workers, ironworkers, engineers, heavy equipment operators, and others labored at the site where the towers had stood, a place now known variously as "Ground Zero" or "the Hole." In the shock and horror that followed the attacks, among the few bright spots were the many tales of heroism told by people who owed their lives to police, fire, and medical personnel.

That heroism continued in the weeks of the cleanup, as rescue workers sifted through piles of wreckage. The purpose of their job was manifold. Not only were they cleaning the site, but they were looking for evidence, and—most poignantly—for any signs of the dead.

At first, rescuers had hoped to find survivors trapped under the rubble and trauma centers at local hospitals braced to treat mass casualties, but those hopes faded quickly, and the cleanup work involved sifting through materials that included physical traces of the building's former inhabitants. Not only was the cleanup work grisly, it was also dangerous: rather than working on solid ground, the rescuers had to set up their cranes and other equipment on top of debris piled several hundred feet above the buildings' foundations.

The numbers of the dead would emerge slowly, and had yet to be fully authenticated even two years later. Although the dead numbered 2801, it was estimated that at the early morning hour, almost 7000 of the 50,000 people who worked in the buildings were in their offices at the time of the attacks. Although the span of time between the attacks and the collapse of the buildings was little more than an hour, it had been enough for those who were able to do so to evacuate via stairwells.

Structural explanations. In late 2001, a team of investigators that included representatives of the American Society of Civil Engineers and the Federal Emergency Management Agency (FEMA) commenced a study on the structural collapse of the towers, the details of which they made public in April 2002. In August 2002, the National Institute of Standards and Technology (NIST) began its own study, scheduled to last two years.

The first team concluded that it was not the impact, but the heat from the burning jet fuel, that heated the temperature of the buildings' steel support structures up to 800°C (1472°F), causing them to buckle and the floors to collapse downward. (Both jets were bound for Los Angeles and had almost a full complement of fuel on board.) On the other hand, the impact did have the effect of knocking out support columns in the building's interior, which may have weakened the structure. The initial crash neutralized sprinkler systems, allowing spread of the fire, which was fed by caches of paper and other flammable materials in offices.

Almost all sources, including government officials, architects, and engineers, agreed on key elements of the building damage. First, it would have been virtually impossible to prevent the destruction of the buildings by aircraft used in the way they were on September 11 as guided missiles. Second, the structural integrity of the buildings that allowed the towers to stand for over an hour after the impacts enabled thousands of people to evacuate. Finally, it was evident that the era of the extremely tall skyscraper was in question. Due to high costs, the construction of very tall buildings had been on the decline in the United States for many years, and the events of 9/11 sealed the fate of some mega-skyscraper projects.

The perpetrators. Federal authorities, using financial records and other materials, had long since identified the al-Qaeda terror network as the perpetrators of the attack. Al-Qaeda was not a new name: it and its leader, Osama bin Laden, had been linked with the August 1998 bombings at U.S. embassies in Africa, and with the bombing of the USS Cole in Yemen in 2000.

Al-Qaeda had strong links to the Taliban regime in Afghanistan, which gave them asylum. Officials in the administration of President George W. Bush, as well as some observers outside the administration, also held that there were substantive links between al-Qaeda, the terrorists who carried out the 1993 bombing, and the government of Iraq. (In fact, Ramzi Youssef, one of the ring leaders in 1993, was nephew to Khalid Sheikh Mohammed, a top al-Qaeda operative, and considerable evidence—including Youssef's Iraqi passport—linked them to Iraq.) The U.S. military actions against Afghanistan in 2001–2002, and Iraq in 2003, were a response to the 2001 terrorist attacks, whose most potent images revolved around the collapse of the World Trade Center towers.



Halberstam, David. New York September 11. New York: Power House Books, 2001.

Hoge, James F., and Gideon Rose. How Did This Happen?: Terrorism and the New War. New York: PublicAffairs, 2001.

One Nation: America Remembers September 11, 2001. Boston: Little, Brown, 2001.

Smith, Dennis. Report from Ground Zero: The Story of the Rescue Efforts at the World Trade Center. New York: Viking, 2002.


Day One—The Attack. Los Angeles Times. < > (April 22, 2003).

September 11, 2001. How Stuff Works. < > (April 22, 2003).

September 11 Archive. < > (April 22, 2003).


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