The Pentagon is the headquarters of the United States Department of Defense

The Pentagon is one of the world's largest office buildings, with about 6,500,000 sq ft, of which 3,700,000 sq ft 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 of corridors. The Pentagon includes a five-acre 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.