Fort Matanzas stands near an inlet south of St. Augustine, where the Matanzas River reaches the Atlantic. The place-name predates the fort. In 1565 Spanish forces killed groups of French Huguenot colonists near the inlet after establishing St. Augustine; matanzas means killings or slaughters in Spanish. Nearly two centuries later, the inlet remained strategically important because an enemy could enter behind the barrier island and approach St. Augustine from the south, bypassing the Castillo de San Marcos and the main harbor defenses.

British colonies to the north increasingly threatened Spanish Florida. South Carolina forces attacked St. Augustine in 1702, and Georgia’s founder James Oglethorpe mounted another major siege in 1740. Although the Castillo held, Spanish governor Manuel de Montiano recognized that the unfortified southern waterway exposed the city. He ordered a watchtower and battery at Matanzas. Enslaved, free, and military laborers quarried and shaped coquina, a local shellstone that could absorb cannon impact, and construction proceeded from 1740 to 1742.

The completed tower was compact but effective. A small garrison operated several cannon from a raised gun deck while living and storing supplies within thick masonry walls. Access depended on ladders and boats, and soldiers endured insects, heat, storms, isolation, and shortages. In 1742 a British force approached the inlet but withdrew after exchanging fire with the new fort. Matanzas never faced a full siege. Its presence, observation post, and artillery closed the southern approach and complemented the much larger Castillo fifteen miles to the north.

Florida passed to Britain in 1763 and returned to Spain in 1783 before becoming United States territory in 1821. Fort Matanzas lost its military purpose and deteriorated in the coastal environment. The War Department carried out repairs in the nineteenth century, while growing historical interest encouraged federal protection. Fort Matanzas National Monument was proclaimed in 1924. Stabilization and restoration preserved the coquina tower, and the protected area expanded to include barrier-island, marsh, dune, and maritime forest ecosystems surrounding the historic structure.

Visitors reach the fort by boat across the river, repeating the waterborne access that defined its operation. The monument also protects archaeological evidence and natural habitat, including nesting and feeding areas for coastal wildlife. Interpretation connects the 1740s fort with the 1565 killings, Spanish and British rivalry, enslaved labor, Indigenous history, and the long defense of St. Augustine. Fort Matanzas is modest in size, yet it reveals a broad Atlantic contest in which geography, shipping routes, colonial violence, and a narrow tidal inlet shaped imperial decisions.