National Park Service, Florida.
Built by the Spanish in St. Augustine to defend Florida and the Atlantic trade route, Castillo de San Marcos National Monument preserves the oldest masonry fortification in the continental United States and interprets more than 450 years of cultural intersections.
On State Route A1A overlooking Matanzas Bay in the heart of the historic district of Saint Augustine, the Castillo is approximately a five mile drive from Interstate 95.