The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia, just across the Potomac River from Washington, D.C. It is a distinctive five-sided building and one of the largest office buildings in the world, designed and constructed during 1941–1943 to consolidate the War Department’s offices and support the military services (Army, Navy, and Air Force). It functions as both a functional workplace and a symbolic center of U.S. national security.