The Pentagon, in Arlington County, Virginia, across the Potomac River from Washington, D.C., is the headquarters of the United States Department of Defense. As a symbol of the U.S. military, the phrase The Pentagon is often used as a metonym for the Department of Defense and its leadership.
The building was designed by American architect George Bergstrom and built by contractor John McShain. Ground was broken on September 11, 1941, and the building was dedicated on January 15, 1943. General Brehon Somervell provided the major motivating power behind the project; Colonel Leslie Groves was responsible for overseeing the project for the U.S. Army.
The Pentagon is the world’s largest office building, with about 6,500,000 sq ft (600,000 m2) of space, of which 3,700,000 sq ft (340,000 m2) are used as offices. Some 23,000 military and civilian employees, and another 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 central five-acre (20,000 m2) pentagonal plaza is nicknamed “ground zero” on the presumption that it would be a prime target in a 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 (59 victims and the five perpetrators on board the airliner, as well as 125 victims in the building), according to the 9/11 Commission Report. It was the first significant foreign attack on Washington’s governmental facilities since the city was burned by the British during the War of 1812.
The Pentagon is listed on the National Register of Historic Places and is a National Historic Landmark.