Castillo de San Marcos is the oldest masonry fort in the continental United States. Only the forts in San Juan, Puerto Rico are older: Castillo de San Felipe del Morro and Castillo de San Cristobal. Castillo de San Marcos guards the Matanzas Bay of the City of St. Augustine, FL. It was begun by the Spanish founders of the city in 1762, almost two hundred years after the city’s founding in 1565 to better protect it from raids by the English and from pirates and to preserve the city as part of the Spanish empire. Sir Francis Drake had attacked the city in 1568, and Robert Searle, an English pirate had attacked it in 1668. The initial forts were built of wood and were not much of a defense against these types of marauders.
The design of the Castillo adheres to the theories of the French engineer Vauban regarding the design of masonry forts to protect against pedestrian, cavalry and seaborne attacks and cannon ball projectiles. Vauban’s theories were valid until about 1880 when the technology of cannons markedly improved by rifling and use of aerodynamic projectiles to the point that masonry forts were obsoleted. The final military invalidation of these types of forts was the inventions of the hot air balloon and the airplane, both of which could be used to bomb from above. Castillo de San Marcos was designed by the Spanish engineer, Ignacio Daza under the direction of Francisco de la Guerra y de la Vega, Commandant.
It is constructed of a unique stone called coquina, mined from the neighboring island of Anastasia from the ‘King’s Quarry’, and ferried to the construction site. The coquina consists of sea creature shells accumulated over multiple millennia similar to limestone. However, this material is initially soft when quarried because there typically isn’t an overburden to compress and densify it like with limestone. It was quarried from the ground with hand tools, but after drying when exposed to air it hardens considerably. After hardening, it retains its porous composition that functions very much like a shock absorber when impacted by cannon balls, as was experienced later when the fort saw action in 1702 when the S. Carolina Colony attacked it, and again in 1740 when the Georgia Colony attacked it
The plan of the fort is a masonry star, with a square Plaza de Armas (parade ground) in the center, surrounded by very thick masonry walls and buildings, which walls are protected on the corners by projecting bastions that are solid masonry with earthen fill, to absorb the brunt of any cannon fire, and shaped in plan to preserve lines angles of fire against any attacker. The Spanish named each of the bastions and the view in this issue’s limited edition print of a sketch by Ladd P. Ehlinger is of the San Pedro Bastion, to the left of the entry bridge as one enters the fort. The other three bastions in clockwise order are, San Pablo, San Carlos, and San Agustin. This surrounding masonry wall is composed of casemate masonry vaults, the deck on top of which were mounted cannon in addition to the cannon within each vault. Other functions were also contained in these vaults, such as kitchen, dining, offices, men’s quarters, powder magazines, etc.
The fort is surrounded by a moat, kept dry by the Spanish until an attack, during which sluice gates were opened to fill it with sea water. On the other side of the moat were various constructions of retaining walls to make it more difficult for attackers to even get to the moat, all typical of a Vauban type design.
After the Treaty of Paris in 1763, the British gained control of St. Augustine as the capital of British East Florida, and the fort was renamed Fort St. Mark until the Peace of Paris in 1783 when Florida was transferred back to Spain. In 1821, Spain ceded Florida to the United States, and we renamed it Fort Marion in honor of Francis Marion, the Revolutionary War hero. The fort was deactivated in 1933 and given to the National Park Service where it remains today as a major tourist attraction and historical monument worth seeing.