Located in Washington D.C., The Pentagon serves as the headquarters of the U.S. Department of Defense. Probably the most recognizable icon of the U.S. armed forces, the term ?Pentagon? is usually used interchangeably with the Department of Defense as opposed to the structure itself.

Before The Pentagon, the U.S. Department of Defense, then known as the U.S. Department of War was housed at Munitions Building, a temporary building situated on the National Mall. When World War II broke out, it was imperative for the Department of War to expand its capacity and then Secretary of War Henry Stimson saw that the armed forces needed a much bigger space to cope with the demands of the war. Stimson brought up the matter to President Franklin Roosevelt and a congressional hearing resolved that the U.S. military needed a permanent space rather than expanding to another temporary structure.

Construction of the Pentagon began on September 11, 1941 in a massive area found across the Potomac River. It took 380,000 tons of sand and gravel dug out of the Potomac River to make the reinforced concrete that was utilized to create the humongous structure. The blueprint of The Pentagon was conceptualized by architect George Begstorm. The building was formally dedicated on January 1943.

Bergstorm?s design was straightforward and stands as the perfect example of space efficiency. A 2-hectare courtyard found at The Pentagon?s hearts is encircled by five pentagonal rings. These five sub-structures were made one at a time and as soon as a wedge was completed, it was immediately occupied. The first tenants moved here in 1942.

It only took 16 months for The Pentagon to be completed and cost $83 million. It instantly became the largest office building in the entire planet with a floor area of 600,000 square meters. It is two times the size of Chicago?s Merchandise Mart which was the biggest office space building before The Pentagon and boasts of three times the usable business space of the Empire State Building in New York. It has an impressive 17.5 miles of walkways distributed among the building?s five floors. However, walking around The Pentagon is not a herculean task. Due to the efficiency of how it was built, getting from one point to another would not consume more than seven minutes.

An interesting fact about The Pentagon is that it did not use marble when it was constructed, which is actually a popular material across all government facilities. This is because when The Pentagon was built during World War II, Italy, which was the source of the finest marbles, was an opponent of the United States.