A view of the Castillo de San Marcos, St Augustine Fl.
The Castillo de San Marcos is the oldest masonry fort in the continental United States (Castillo San Felipe del Morro in San Juan, Puerto Rico is older). Located on the western shore of Matanzas Bay in the city of St. Augustine, Florida, the fort was designed by the Spanish engineer Ignacio Daza.
Construction began in 1672, 107 years after the city's founding by Spanish Admiral and conquistador Pedro Menéndez de Avilés, when Florida was part of the Spanish Empire. The fort's construction was ordered by Governor Francisco de la Guerra y de la Vega after the destructive raid of the English privateer Robert Searles in 1668. Work proceeded under the administration of Guerra's successor, Manuel de Cendoya in 1671, although the first stone was not laid until 1672.
After Britain gained control of Florida in 1763 pursuant to the Treaty of Paris, St. Augustine became the capital of British East Florida, and the fort was renamed Fort St. Mark until the Peace of Paris (1783) when Florida was transferred back to Spain. In 1819 Spain signed the Adams–Onís Treaty which ceded Florida to the United States in 1821; consequently the fort was designated a United States Army base and renamed Fort Marion, in honor of American Revolutionary War hero Francis Marion. The fort was declared a National Monument in 1924, and after 251 years of continuous military possession, was deactivated in 1933. The 20.48-acre (8.29 ha) site was then turned over to the United States National Park Service. In 1942 the original name Castillo de San Marcos, was restored by an Act of Congress.
Castillo de San Marcos was twice besieged: first by English colonial forces led by Carolina Colony Governor James Moore in 1702, and then by Georgia colonial Governor James Oglethorpe in 1740. Possession of the fort has changed six times, all peaceful, amongst four different governments: the Spanish Empire, the Kingdom of Great Britain, the Confederate States of America and the United States of America (Spain and the United States having possession two times each).
Under United States control the fort was used as a military prison to incarcerate members of Native American tribes starting with the Seminole—including the famous war chief, Osceola, in the Second Seminole War—and members of western tribes, including Geronimo's band of Chiricahua Apache. The Native American art form known as Ledger Art had its origins at the fort during the imprisonment of members of the Plains tribes such as Howling Wolf of the southern Cheyenne.