Once again, the coquina walls held firm. Spanish defenders withstood bombardments and raids, while supply lines from Cuba kept them provisioned. After weeks of frustration, Oglethorpe abandoned the siege, unable to crack the fortress.
These repeated failures convinced Britain that direct conquest of St. Augustine was nearly impossible without massive resources. The Castillo became a symbol of Spanish resilience on the southeastern frontier.
Shifting Empires: British Control, 1763–1783
The fortunes of Castillo de San Marcos changed not through battle but diplomacy. In 1763, at the conclusion of the Seven Years’ War, Spain ceded Florida to Britain in exchange for Havana, which the British had captured.
Under British control, the fort was renamed Fort St. Mark. The British garrison used it as a base to secure East Florida, which had become a haven for Loyalists fleeing the American Revolution. During this period, the fort witnessed relatively little combat, but it played an important role as Britain sought to stabilize its southern colonies.
In 1783, with the Treaty of Paris ending the American Revolution, Britain returned Florida to Spain. The Castillo resumed its Spanish name and continued to guard St. Augustine shutdown123