Castillo de San Marcos, Masonry star fort in St. Augustine, Florida, United States
The Castillo de San Marcos is a masonry fortification on the western shore of Matanzas Bay in St. Augustine, Florida. Four diamond-shaped bastions form the corners of the structure, whose walls are built from pale shell limestone and measure several meters thick.
Spanish engineers began work in 1672 after earlier wooden defenses were destroyed during attacks and completed construction in 1695. The structure served as a stronghold protecting Florida and the Atlantic trade route.
The fort's name honors Saint Mark, and it was renamed Fort Marion from 1821 to 1942 after Francis Marion. Under U.S. control it held Seminole prisoners including Osceola, and Plains captives such as Howling Wolf produced Ledger Art drawings here. Twenty Seminole prisoners escaped through an infantry embrasure in 1837.
The fortress sits centrally in St. Augustine and is reachable on foot from most lodgings in the old town. The ramparts offer shaded passages and open viewpoints, so comfortable footwear and sun protection are recommended for warm days.
The walls made from shell limestone act like a sponge, absorbing cannonballs instead of splintering or cracking. This natural property made the material an unusual choice and gave the fortress unexpected resistance to artillery fire.
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