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Castillo San Marcos in St. Augustine is Florida's dominant Spanish Colonial landmark and the oldest masonry fort in the United States. Construction of the fortress, which began in 1672, took a quarter century and was completed in 1696. With walls 16 feet thick at the base and protected by moat, the Castillo was never taken by force. In 1763, as a provision of the Treaty of Paris (1763), Britain gained all of Florida in exchange for returning Havana and Manila to Spain, captured during the Seven Years' War and the fort was renamed Fort St. Mark until 1784. At the end of the American Revolution war, the Second Treaty of Paris returned Florida to Spain. Spain signed the Adams-Onis Treaty in 1819 ceding Florida to the United States and the fort was renamed Fort Marion. In 1924, the fort was designated a National Monument and in 1933 it was transferred to the National Park Service from the War Department. In 1942, in honor of its Spanish heritage and construction, the fort was once again given its original name of Castillo de San Marcos.