The Cambridge Common Historic District is a historic district encompassing one of the oldest parts of Cambridge, Massachusetts. It is centered on the Cambridge Common, which was a center of civic activity in Cambridge after its founding in 1631. It was the site of the election for governor of the Massachusetts Bay Colony in 1636, and was a military barracks site during the American Revolutionary War. The common was gradually reduced in size to its present roughly triangular shape, and surrounded by buildings in the 18th and 19th centuries. In 1973 a historic district encompassing the extant common and everything within 100 feet (30 m) of it was listed on the National Register of Historic Places. In 1987 the district was amended to rationalize the boundary, which overlapped adjacent distric