Castillo de San Marcos served as a fort for more than 205 years. Built between 1672 and 1695 by the Spanish, it protected the newly established territory of Spanish Florida from the British and pirates. It’s the oldest masonry fortification in the U.S., as well as the only surviving 17th-century military site in the country. Additionally, it is one of only two forts in the world constructed from coquina, a semi-rare limestone composed of shell fragments. Though the Spanish maintained control of the Castillo de San Marcos for most of its military career, it was used by the British during the American Revolution and by Confederate and Union soldiers during the Civil War. The fort became a national monument in 1900.
