The September 11th attacks (often referred to as nine-eleven, written 9/11) were a series of coordinated suicide attacks by al-Qaeda upon the United States on September 11, 2001. On that morning, 19 al-Qaeda terroristshijacked four commercial passenger jet airliners. The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City, instantly killing everyone on board and a number of others working in and around the buildings. Because of structural damage caused by the collisions and the ensuing fires, both buildings collapsed within two hours, destroying nearby buildings and damaging others. This subsequently resulted in the death of more than 2,600 people- those trapped inside, others trying to escape, and the rescue workers, such as the fire fighters and police officers, rushing to their aid. A third hijacked airplane flew into the Pentagon killing hundreds of more people. The fourth plane was crashed into a field (grassland) near Shanksville in rural Somerset County, Pennsylvania as some of its passengers and flight crew fought to retake control of the plane which hijackers had redirected toward Washington, D.C. The passengers of Flight 93 reportedly made the decision to forcibly regain control from the terrorists after cell phone calls to loved ones. During those conversations, the hostages learned of the prior attacks of the day. There were no survivors from any of the flights. In addition to the 19 suicide hijackers, 2,975 people were killed as a direct result of the terrorist attacks. Another 24 were missing and presumed dead, while untold thousands were injured or disabled. September 11th or 9/11 is widely acknowledged as a landmark in the historical calendar.
The design and construction of the World Trade Center twin towers involved many other innovative techniques, such as the slurry wall for digging the foundation, and wind tunnel experiments. Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969. Extensive use of prefabricated components helped to speed up the construction process. The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972. Four other, low-level buildings were constructed as part of the World Trade Center in the 1970s, and a seventh building was constructed in the mid-1980s. (more...)