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08/17/2024 Imperial Invasion of Castillo de San Marcos, St. Augustine, FL (big Florida Garrison event to "occupy" the Castillo de San Marcos National Monument, for filming & photo ops). The Castillo is the oldest masonry fortification in the continental United States. The Castillo has had two major construction periods, from 1672 to its initial completion in 1695, and again from 1738 to 1756. The Castillo is made of coquina, a soft limestone made up of broken shells and sand cemented together by calcium carbonate, essentially creating a natural form of concrete. For more information about the Castillo, see the National Park Service webpage: https://www.nps.gov/casa/index.htm