Fort Mifflin, originally called Fort Island Battery and also known as Mud Island Fort, is Philadelphia's only fort. It was commissioned in 1771 and sits on Mud Island on the Delaware River below Philadelphia, Pennsylvania near Philadelphia International Airport.
During the American Revolutionary War, the British bombarded and ultimately captured the fort as part of their conquest of Philadelphia in autumn 1777. The United States Army began to rebuild the fort in 1794 and continued to garrison and build on the site through the 19th century. It housed prisoners during the American Civil War. The army decommissioned Fort Mifflin in 1954 and the City of Philadelphia took ownership of the property in 1962. The fort was restored by historic preservationists, and provides many historic and educational programs today, as well as unique events. The fort is managed by Fort Mifflin on the Delaware, the non-profit organization responsible for continuing the Fort's restoration and preservation as a historic site.