Built in 1695, the Castillo de San Marcos National Monument was constructed by the Spanish to defend Florida and the Atlantic Trade Route and is the oldest masonry fort in the United States. The impressive structure is a symbol of the cultural and imperial struggles that would shape North America in its infancy. Never captured in battle, its coquina walls are a testament to the endurance of the nation’s Hispanic heritage and other cultural groups that are part of its story.

Following Sir Francis Drake’s attack of the city in 1586 and pirate John Davis’ 1668 raid, the Spanish requested funds from Spain and Mexico to build a permanent defense. The Spanish crown approved the stone fortress and construction began in 1672.

The design is based on 17th-century Italian bastions which lowers castle walls with mounds of earth around the exterior to reinforce the walls. Circular towers at each corner of the fort protect from vulnerable land and water attacks. The moat and drawbridges further secure access into the castle.

The walls of the Castillo de San Marcos are 14-feet thick and made of coquina, a soft limestone made of broken shells native to St. Augustine and mined in quarries on Anastasia Island. Its strength was put to the test during the War of Spanish Succession in 1702. The softness of the coquina absorbed the impact of cannonballs so the structure never cracked or crumbled. The Castillo was the only structure in St. Augustine to survive English fire which led the Spanish to extend the castle’s walls for inner defense lines, known as the Cubo and Rosario Lines. Today, the Cubo line is replicated with wood and includes the coquina City Gates, and the Rosario line is used as Cordova Street.

In fact, the Castillo de San Marcos is only one of two forts built from coquina. The second is Fort Matanzas, completed in 1742 and located just 15 miles south of St. Augustine on the Matanzas River.