The District of Columbia, The capital of the USA.
Washington, D.C. was designed by Major Pierre Charles L'Enfant around 1791. It was the first American city planned for a specific purpose. It was designed to be a beautiful city with wide streets and many trees. The city's business is centered around the government. Another name for Washington, D.C. is the District of Columbia. The district was originally a 10 miles square crossing the Potomac River into Virginia. Both Virginia and Maryland donated part of their land for the capital district. The Virginia portion of D.C. was later ceded back to Virginia.
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The Pentagon—a building, institution, and symbol—was conceived at the request of Brigadier General Brehon B. Sommervell, Chief of the Construction Division of the Office of the Quartermaster General, on a weekend in mid-July 1941. The purpose was to provide a temporary solution to the War Department’s critical shortage of space.The groundbreaking ceremony took place on September 11, 1941. The building was dedicated on January 15, 1943, nearly 16 months to the day after the groundbreaking.
Here are a couple of pictures of the Pentagon.