The Pentagon was designed to consolidate more than 24,000 civilian and military personnel in 17 War Department buildings scattered throughout metropolitan Washington, DC. In four days during the summer of 1941, G. Edwin Bergstrom, a dollar-a-year volunteer architect, completed drawings and specifications for a building to accommodate as many as 40,000 people. Under the Army Corps of Engineers, up to 13,000 workers  spread over three shifts, seven days a week  built the Pentagon in only 16 months. On September 11, 2001, exactly 60 years after groundbreaking on the site, terrorists crashed a Boeing 757 into the Pentagons outer west wall. Within a year, the wall was repaired.
One of the worlds largest office buildings, the Pentagon has three times the floor space of the Empire State Building. The five-sided building covers 29 acres and contains 17.5 miles of corridors within its five floors, mezzanine and basement. The Pentagon was designated a National Historic Landmark on October 5, 1992.