On Sept. 11, 1941, construction of the US military’s headquarters — The Pentagon — begins with a ground-breaking ceremony on the site of the Hoover Field in Arlington, Va., that closed in June. The building came be be five-sided because it was initially to be located on a nearby plot of land that was an irregular pentagon. When the site was moved, the building — designed by architect George Bergstrom — was made symmetrical with five sides, five floor, five rings and two basements. It was finished on Jan. 15, 1943.
Because of wartime limitations on the use of steel, the building was constructed by the Philadelphia construction firm John McShain of reinforced concrete — using nearly 700,000 tons of sand dredged from the nearby Potomac River — with an Indiana limestone facing. The building was to have been built for about $31 million, but cost twice as much.
To this day, it remains the the world’s largest single office building by floor area with some 5 million square feet of office space that accommodates 26,000 military, civilian and support personnel.
The project manager was Col. Leslie Groves of the Army Corps of Engineers, who the following year was selected to head America’s top secret effort to develop an atom bomb, the Manhattan Project.
The building was designed and initially built in accordance with Virginia’s racial segregation laws, with separate dining and toilet facilities for blacks and whites. As a result, the building was twice as many bathrooms as necessary for a building its size.
The Pentagon was renovated one wedge at a time between 1998 and 2011 with new blast resistant windows, reinforcing as well as better fire fighting systems.
On Sept. 11, 2001, hijackers flew American Airlines Flight 77 into the recently renovated western wedge of the building, killing all 64 aboard the Boeing 757, as well as 125 in the building. Despite an intense fire, those renovations kept the building from collapsing for half an hour, allowing hundreds to escape.