How Did the Pentagon Get Its Five-Sided Shape?

In 1941, with World War II raging in Europe, the United States made plans to consolidate personnel in its War Department, which had 24,000 employees working out of 17 different buildings around the District of Columbia. Lt. Col. Hugh Casey was tasked with designing a building that would fit on a five-sided parcel of land near Arlington National Cemetery, and house a staff of 40,000. Architects came up with a pentagonal plan that would fit the site perfectly. Each of the five wedges of the 29-acre structure would feature concentric rings of office space, linked by 17.5 miles (28 km) of corridors, with a courtyard in the center. Officials ultimately decided to construct the building on a different site in Northern Virginia, but they kept the Pentagon’s unique shape.

An office building like no other:

• In January 1943, after 17 months of construction, the Pentagon was ready for duty. Its 6.4 million square feet (594,579 square meters) of space still makes it the world’s largest low-rise office building.
• During World War II, messengers used bikes and roller skates to get around quickly. Later, electric vehicles helped shuttle people -- until one knocked down and injured the Secretary of the Air Force in the 1960s.
• On 11 September 2001, five hijackers slammed American Airlines Flight 77 into the Pentagon, killing 64 people on the plane and 120 Pentagon employees.