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Located on 20 acres in the city of St. Augustine, Florida, the Castillo de San Marcos National Monument is primarily an urban-based park with little natural vegetation. Built in the late 1600s as a fortress of the Spanish Empire, the Castillo was built to protect the settlement of St. Augustine and the Atlantic trade route from British forces and raiding pirates. After years of alternating between Spanish and British control, the Castillo was purchased by the United States in 1821 and used by the U.S. army until 1899. Today, the Castillo represents the oldest and largest masonry fortress within the continental United States.
Source: NPS DataStore Collection 7765 (results presented are a subset). To search for additional information, visit the NPS DataStore.
Last updated: January 1, 2026