Governors Island is a 172-acre island located a half-mile from the southern tip of Manhattan in New York harbor. Its name comes from the time when New York was a British colony and the colonial assembly reserved the island for the exclusive use of New York’s royal governors. When the American Revolution began in 1776, George Washington ordered the island to be fortified with earthworks just prior to the Battle of Long Island (also known as the Battle of Brooklyn) - the first ever engagement of the fledgling Continental Army with British forces. Two fortifications were placed on Governors Island in the years preceding the War of 1812 as part of an extensive coastal defense system. During the Civil War, Castle Williams held Confederate prisoners of war. After the war, it was used as a military stockade and became the east coast counterpart to military prisons at Fort Leavenworth, Kansas and Alcatraz Island in San Francisco Bay. In 1878 the military installation on the island, then known as Fort Columbus, became a major Army administrative center and, in 1939, the headquarters of the United States First Army. When the Army left Governors Island in 1966, the installation became a U.S. Coast Guard base - the largest in the world. Its closing in 1997 concluded almost two centuries of the island’s use as a federal reservation. In 2001, the two historic fortifications and their surroundings became a national monument.