<Tr> <Th> Added to NRHP </Th> <Td> July 27, 1988 </Td> </Tr> <Tr> <Th> Designated VLR </Th> <Td> April 18, 1989 </Td> </Tr> <P> The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia, across the Potomac River from Washington, D.C. As a symbol of the U.S. military, The Pentagon is often used metonymically to refer to the U.S. Department of Defense . </P> <P> The Pentagon was designed by American architect George Bergstrom (1876--1955), and built by general contractor John McShain of Philadelphia . Ground was broken for construction on September 11, 1941, and the building was dedicated on January 15, 1943 . General Brehon Somervell provided the major motive power behind the project; Colonel Leslie Groves was responsible for overseeing the project for the U.S. Army . </P>

What is the main purpose of the pentagon