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The Pentagon building, an institution and an iconic symbol, is the headquarters of the Department of Defense (DoD). The Pentagon's three occupant groups–military, civilians, and contractors–contribute to the planning and execution of the defense of our country. The Pentagon is one of the world's largest and most recognizable office buildings. It is twice the size of the Merchandise Mart in Chicago; it has three times the floor space of the Empire State Building in New York; and the National Capital could fit into any one of the five wedge-shaped sections. The Pentagon is virtually a city in itself. In terms of population, the Pentagon's 25,650 employees make it larger than nine out of 10 towns in the United States.
The Pentagon, originally known as "Arlington Farms," began construction on September 11th, 1941 (exactly 60 years prior to the 9/11 attacks) on a plot of land which was once part of the grand estate of the Confederate general Robert E. Lee, before its confiscation during the Civil War. The Pentagon was conceived at the request of Brigadier General Brehon B. Sommervell, Chief of the Construction Division of the Office of the Quartermaster General. The original purpose of the Pentagon was to provide a temporary solution to the War Department's critical shortage of space. Post WWII plans were to recycle the Pentagon into hospital, office, or warehouse space. The site designated for construction was bordered by five roadways which dictated the concept for a Pentagon-shaped building. In addition to the 296 acres the Federal government owned, an additional 287 acres (including the old Hoover Airport and a low income residential area called "Hell's Bottom") were purchased. The total cost to develop the Pentagon Reservation was over $83 million, which included about $2.25 million to purchase land, $33.40 million to construct outside facilities and the Pentagon Lagoon, and $49.60 million to construct the Pentagon. The 16 month project required the skill of 1,000 architects and the labor of 14,000 tradesmen (on three shifts, 24 hours a day). At the height of WWII, the Pentagon housed over 33,000 occupants.
In 1992, the building was designated as a National Historic Landmark with five outer facades obtaining historic status: the Central Courtyard and its surrounding facade; the Terrace fronting the Mall Entrance; the terrace fronting the River Entrance; and the Pentagon's distinctive five-sided shape.