The Pentagon in Arlington, Virginia, serves as the headquarters of the United States Department of Defense and as a powerful symbol of the American military. Built with wartime speed between 1941 and 1943, it unified scattered War Department offices in a vast five-sided complex of reinforced concrete, designed by George Bergstrom and advanced by Henry L. Stimson and Brehon Somervell. Its immense scale, efficient ring-and-radial plan, and distinctive form made it one of the world’s largest office buildings. Its history also includes the 11 September 2001 attack, after which memorials were added. The building remains central to U.S. defense administration and national memory.