- Designer: Swedish American architect George Bergstrom (1876 – 1955)
- Builder: John McShain, a general contractor from Philadelphia, Pennsylvania
- Ground Breaking: September 11, 1941
- Completed: January 15, 1943
- National Historic Landmark: 1992
The Pentagon in Arlington, Virginia is headquarters of the United States Department of Defense and one of the largest low-rise office building in the world. Set in a five-acre hexagon-shaped plaza, the Pentagon houses about 23,000 military and civilian employees and about 3,000 non-defense workers. The building is called the Pentagon because it has five sides. The shape of the building was designed to accommodate a different building lot. The location was changed, but the design remained the same.
The floor plan of the Pentagon echoes its shape. The Pentagon has five floors above ground, plus two basement levels. Each floor has five rings of corridors. As a whole, the Pentagon has some 17.5 miles (28.2 km) of corridors.
September 11 Terrorist Attack at the Pentagon
On September 11, 2001, five terrorists hijacked American Airlines Flight 77 and crashed it into the west side of the Pentagon building. The crash killed all 64 people on the plane and 125 people inside the building. The impact of the crash caused partial collapse of the west side of the Pentagon. A September 11 Pentagon Memorial has been built to honor those who died.