San Juan de Ulua

San Juan de Ulúa began as a modest fort in 1535 on a low coral island guarding the entrance to the port of Veracruz, and was rebuilt in stages through the 16th to 18th centuries into the largest fortification Spain built in the Americas. Its coral-block walls, moat, and bastions were designed to protect the annual treasure fleet that carried silver from New Spain to Seville, and the fort withstood attacks by English privateer John Hawkins in 1568 and a French raid in 1683. After Mexican independence in 1821, a Spanish garrison held out inside the fortress until 1825, making it the final piece of Spanish territory on the mainland. Through the 19th century the complex served as a state prison, holding both common criminals and political prisoners such as Benito Juárez, and its damp, windowless cells are preserved as part of the visit. The fort was also bombarded by French forces in 1838 and occupied twice by United States forces, in 1847 and 1914. Visitors today walk through the fortress's bastions, the vaulted powder magazines, the former governor's residence, and the notorious dungeon known as El Purgatorio, where iron rings and low stone cells remain visible. Interpretive panels, arranged as a chronological route from the 16th-century core to the 19th-century prison wings, trace the fortress's shift from military outpost to penal colony to national monument. Conservation work led by Mexico's national anthropology institute has stabilized the coral masonry and drainage system, though salt erosion from the harbor remains an ongoing maintenance concern. The causeway connecting the island to the mainland, built in the early 20th century, replaced the boat crossing that once isolated prisoners from escape.