The Pentagon contains 6.5 million square feet situated on approximately 34 acres, including its 5-acre central courtyard. It has five stories above ground and two basement levels under ground. Its corridors run 17.5 miles. The Pentagon is the largest office building in the world.
The Pentagon was built in less than a year beginning in July 1941. At that time, the United States was preparing to enter World War II, and the Department of War needed more office space. The head of construction for the U.S. Army, Brehon Somervell, wanted to build a headquarters with 4 million square feet, but there was no site in Washington, D.C. big enough for such a building, given that he could not build higher than four stories. When an oddly-shaped, five-sided plot of land was found in Virginia, the building was built to fit the site.