Castle Williams is a circular fortification of red sandstone on the northwest point of Governors Island, part of a system of forts designed and constructed in the early 19th century to protect New York City from naval attack. It is a prominent landmark in New York Harbor. Together with Fort Jay, it is managed by the National Park Service as part of Governors Island National Monument. Design and construction Castle Williams was designed and erected between 1807 and 1811 under the direction of Lieutenant Colonel (later Colonel) Jonathan Williams, Chief Engineer of the Corps of Engineers and first Superintendent of the United States Military Academy at West Point, New York. Williams was also a relative of Benjamin Franklin. The castle was one component of a defensive system for the inner harbor that included Fort Columbus (later renamed Fort Jay) and the South Battery on Governors Island; Castle Clinton at the southern tip of Manhattan, Fort Wood on Liberty Island, and Fort Gibson on Ellis Island. Its pioneering design consisted of multiple levels of enclosed or fortified gun emplacements (casemates). It established a prototype for American coastal fortification design for the rest of the 19th century. The nearly circular fortification, 40 feet high and 210 feet in diameter, was constructed of sandstone walls 7 to 8 feet thick. Each of its four levels had 13 casemates (or pairs of barbette mounts on the fort's roof) that could hold 26 cannons of varied caliber. The four-tier arrangement was only duplicated in the US by Battery Weed at Fort Wadsworth on Staten Island and Fort Point in San Francisco. However, at Castle Williams the third tier was intended as barracks and was not armed. Before its completion, Colonel Henry Burbeck, commanding the defenses of New York City, issued an Army order on November 24, 1810, that named the castle for its designer and builder: "In future the Stone Tower on this Island (by the approbation of the Secretary of War) will bear the name of CASTLE WILLIAMS, in honor of the commandant of the United States Corps of Engineers, who designed and erected it." Civil War During the Civil War, the casemates of Castle Williams were used to house newly recruited Union troops, to serve as a barracks for the garrison's troops, and to imprison Confederate enlisted men and deserters from the Union Army. After 1865, it became a low-security military prison that