September 11, 2001 was a dark day in the history of the United States of America and transformed the lives of so many across the globe. The damage caused to property, commerce and shattered lives is almost too difficult to calculate. The most obvious damage came from the lives lost (2996 people died) and for their families, who were left in mourning. Second, was the physical and economic damage: according to the NYC Comptroller, repairs cost approximately $55 billion. The estimated economic impact ranges anywhere from $40 billion to $123 billion. In a series of coordinated attacks on three of America's greatest symbols of strength, Al Qaeda, the organization behind the attacks, meant to break the spirit of the American people. These terrorists targeted the U.S. Capitol, The Pentagon, and the World Trade Center's Twin Towers. On the early morning of September 11, four U.S. commercial jets were taken over by a total of 19 hijackers. American Airlines (Flight 11) was the first plane to take off, and the first to crash into the North Tower of the World Trade Center. It hit the upper floors of the tower at 8:46 am, creating a hole that extended from the 92nd to 98th floors. A second plane, United Airlines (Flight 175), crashed into the South Tower only nineteen minutes later, creating a whole in the building that spanned from the 75th to 84th floors. Both towers were immediately engulfed in a massive cloud of black smoke at the crash site. Pedestrians on NYC streets stopped in their tracks, their attention diverted by the sound of explosions, trembling ground and smoke emanating from the towers. Inside, a blazing inferno was slowly destroying the internal structure of the buildings. Many of those who survived the explosion of the planes were forced to jump from higher floors to avoid a most certain death from intense smoke or flames from the fire. The NYC Fire and Police Departments did their best to coordinate the evacuation the buildings as the fire razed on. Unfortunately, many would lose their own lives trying to prevent further casualties. What came next shocked ordinary people and experts alike; 47 minutes (9:59 am) after the 2nd plane hit the South Tower it suddenly collapsed. The North Tower, which had been hit first withstood the impact intil 10:28 am, but it too fell. As the towers collapsed, people began to run away from the wave of dark ash and debris pouring into the streets like a tsunami. The surreal scene would be etched into their memories forever. A total of 2,606 (including 147 airline passengers and hijackers) lost their lives in the World Trade Center disaster. Many wondered how these towers, a feat in engineering, were unable to withstand the impact of the planes. However, most experts agree that it was not the plane's crash that made both towers fall, but the kerosene fuel that exploded upon its impact. Kerosene, burns at much higher temperatures than regular fires. Furthermore, aluminum from the plane also contributed to higher temperature of the fire. Aluminum, especially when surrounded by concrete could reach temperatures as high as 1800 degrees celsius. The molten metal liquid could have easily damaged many of the beam joints that held the building together. Separately in Arlington, Virginia, the south side of the Pentagon was hit by American Airlines (Flight 77) at approximately 9:39 am. All 59 passengers on board were killed upon impact; inside the Pentagon 125 people were killed by the crash and fire that ensued. A fourth plane, United Airlines (Flight 93) was the only plane that did not manage to reach its intended destination. The hijackers who boarded the plane intended to crash it into the U.S. Capitol building. However, their plan was thwarted by passengers that fought back. A twenty minute delay at the airport in Newark gave people on the plane enough time to learn of the events in New York. Soon after the hijackers took over the cockpit, passengers made a decision to revolt, even though it would lead to crashing of plane into the ground. At approximately 10:03, 20 minutes away from Washington D.C, Flight 93 crashed into a field in Somerset County, Pennsylvania. All 44 passengers (including the hijackers) were killed. Soon after the September 11 attacks, recovery plans were put into action. The Pentagon was repaired within a year. Additional buildings on the WTC site were demolished due to the irreparable damage they sustained. The WTC site, often referred to as Ground Zero, is still under construction, but has come a long way. One WTC or the "Freedom Tower" became the tallest building in the western hemisphere in 2013. After its completion, construction will begin on three other buildings at the WTC site. Several memorials have been built over the years. At Ground Zero, two reflecting pools located on the original location of the twin towers commemorate the lives lost on 9/11 and during the 1993 World Trade Center bombing. "Reflecting absence" the official name of the memorial, won the WTC site memorial competition in 2004. It was opened for the public on September 12, 2011. A second memorial, called 'Tribute in Lights' is an installation of two columns of blue light that have been launched every September 11, since 2002. In 2008, the Pentagon memorial was also opened in Arlington County, Virginia. It consists of 183 lit benches, for the 183 victims that died at the Pentagon on September 11. There is also a memorial for Flight 93 victims located in Shanksville, Pennsylvania, where the United Flight 93 originally crashed.