St. Augustine was established in 1565. It is the oldest permanent European settlement in the continental United States. For 235 years it was the political and military capital of the Spanish Province of Florida.
Spanish navigators knew that the best return route to Europe from rich Caribbean possessions was along the Gulf Stream, through the Bahama Channel, and past the shores of Florida. To protect the sea route for galleons laden with tobacco, sugar, chocolate, silver and gold returning to Spain, the Castillo de San Marcos was built in 1672-1695. This hollow square fortress with diamond-shaped bastions served as a northernmost outpost of the Spanish Empire in the New World. During the 18th century, the Castillo went from Spanish control to British and back to the Spanish, who remained in power in Florida until the area was purchased by the United States in 1821.