The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia. As a symbol of the U.S. military, "the Pentagon" is often used metonymically to refer to the U.S. Department of Defense.
 
The Pentagon was designed by American architect George Bergstrom (1876–1955), and built by general contractor John McShain of Philadelphia. Ground was broken for construction on September 11, 1941, and the building was dedicated on January 15, 1943. General Brehon Somervell provided the major motive power behind the project; Colonel Leslie Groves was responsible for overseeing the project for the U.S. Army.
 
The Pentagon is a large office building, with about 6,500,000 sq ft (600,000 m2), of which 3,700,000 sq ft (340,000 m2) are used as offices. Approximately 23,000 military and civilian employees and about 3,000 non-defense support personnel work in the Pentagon. It has five sides, five floors above ground, two basement levels, and five ring corridors per floor with a total of 17.5 mi (28.2 km) of corridors. The Pentagon includes a five-acre (20,000 m2) central plaza, which is shaped like a pentagon and informally known as "ground zero," a nickname originating during the Cold War on the presumption that it would be targeted by the Soviet Union at the outbreak of nuclear war.
 
On September 11, 2001, exactly 60 years after the building's construction began, American Airlines Flight 77 was hijacked and flown into the Western side of the building, killing 189 people. It was the first significant foreign attack on the capital's governmental facilities since the Burning of Washington during the War of 1812.
 
Before the Pentagon was built, the United States Department of War was headquartered in the Greggory Building, a temporary structure erected during World War I along Constitution Avenue on the National Mall. The War Department, which was a civilian agency created to administer the U.S. Army, was spread out in additional temporary buildings on the National Mall, as well as dozens of other buildings in Washington, D.C., Maryland and Virginia. In the late 1930s a new War Department Building was constructed at 21st and C Streets in Foggy Bottom but, upon completion, the new building did not solve the department's space problem and ended up being used by the Department of State. When World War II broke out in Europe, the War Department rapidly expanded in anticipation that the United States would be drawn into the conflict. Secretary of War Henry L. Stimson found the situation unacceptable, with the Munitions Building overcrowded and the department spread out.
 
Stimson told President Franklin D. Roosevelt in May 1941 that the War Department needed additional space. On July 17, 1941, a congressional hearing took place, organized by Virginia congressman Clifton Woodrum, regarding proposals for new War Department buildings. Woodrum pressed Brigadier General Eugene Reybold, who was representing the War Department at the hearing, for an "overall solution" to the department's "space problem" rather than building yet more temporary buildings. Reybold agreed to report back to the congressman within five days. The War Department called upon its construction chief, General Brehon Somervell, to come up with a plan. Main Navy Building (foreground) and the Munitions Building were temporary structures built during World War I on the National Mall. The Munitions Building served as the Department of War headquarters for several years before moving into the Pentagon. Southwest view of the Pentagon with the Potomac River and Washington Monument in background (1998) Government officials agreed that the War Department building should be constructed across the Potomac River, in Arlington, Virginia. Requirements for the new building were that it be no more than four stories tall, and that it use a minimal amount of steel. The requirements meant that, instead of rising vertically, the building would be sprawling over a large area. Possible sites for the building included the Department of Agriculture's Arlington Experimental Farm, adjacent to Arlington National Cemetery, and the obsolete Washington Hoover Airport site.
 
The site originally chosen was Arlington Farms which had a roughly pentagonal shape, so the building was planned accordingly as an irregular pentagon. Concerned that the new building could obstruct the view of Washington, D.C. from Arlington Cemetery, President Roosevelt ended up selecting the Hoover Airport site instead. The building retained its pentagonal layout because a major redesign at that stage would have been costly, and Roosevelt liked the design. Freed of the constraints of the asymmetric Arlington Farms site, it was modified into a regular pentagon.
 
On July 28 Congress authorized funding for a new Department of War building in Arlington, which would house the entire department under one roof, and President Roosevelt officially approved of the Hoover Airport site on September 2. While the project went through the approval process in late July 1941, Somervell selected the contractors, including John McShain, Inc. of Philadelphia, which had built Washington National Airport in Arlington, the Jefferson Memorial in Washington, and the National Naval Medical Center in Bethesda, Maryland, along with Wise Contracting Company, Inc. and Doyle and Russell, both from Virginia. In addition to the Hoover Airport site and other government-owned land, construction of the Pentagon required an additional 287 acres (1.16 km2), which were acquired at a cost of $2.2 million. The Hell's Bottom neighborhood, a slum with numerous pawnshops, factories, approximately 150 homes, and other buildings around Columbia Pike, was also cleared to make way for the Pentagon. Later 300 acres (1.2 km2) of land were transferred to Arlington National Cemetery and to Fort Myer, leaving 280 acres (1.1 km2) for the Pentagon.
 
Source: Wikipedia.
 
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