Fort Jay, a coastal star fort and the name of the former Army post, is located on Governors Island in New York Harbor. Fort Jay is the oldest defensive structure on the island, and was named for John Jay, a member of the Federalist Party, New York governor, Chief Justice of the Supreme Court, Secretary of State, and one of the "founding fathers" of the United States. It was built in 1794 to defend Upper New York Bay, but has served other purposes. From 1806 to 1904 it was named Fort Columbus, presumably for explorer Christopher Columbus. The National Park Service administers Fort Jay together with Castle Williams as the Governors Island National Monument.