Pentagon, the, building accommodating the U.S. Dept. of Defense. Located in Arlington, Va., across the Potomac River from Washington, D.C., the Pentagon is a vast five-sided building designed by Los Angeles architect G. Edwin Bergstrom. It consists of five concentric pentagons connected to each other by corridors and covering an area of 34 acres (13.8 hectares). Completed in 1943, it was intended to consolidate the various offices of the U.S. War Dept., now the Dept. of Defense. Extensive renovations (1994–2011) have modernized and replaced much of the original building. One side of the vast building was damaged by a terrorist attack (Sept. 11, 2001) in which a hijacked airplane was intentionally crashed into the Pentagon. As a result of the crash and subsequent fire 189 people were killed, including the passengers and crew of the jetliner. The attack was coordinated with a similar one on the twin towers of the World Trade Center.
See S. Vogel, The Pentagon: A History (2007).