Castillo de San Marcos

The Castillo de San Marcos is the most seasoned brick work stronghold in the mainland United States (Castillo San Felipe del Morro in San Juan, Puerto Rico is more seasoned). Situated on the western shore of Matanzas Bay in the city of St. Augustine, Florida, the post was composed by the Spanish engineer Ignacio Daza. Construction started in 1672, 107 years after the city's establishing by Spanish Admiral and conquistador Pedro Menéndez de Avilés, when Florida was a piece of the Spanish Empire. The stronghold's development was requested by Governor Francisco de la Guerra y de la Vega after the ruinous strike of the English privateer Robert Searles in 1668. Work continued under the organization of Guerra's successor, Manuel de Cendoya in 1671, in spite of the fact that the primary stone was not laid until 1672.

After Britain picked up control of Florida in 1763 in accordance with the Treaty of Paris, St. Augustine turned into the capital of British East Florida, and the fortress was renamed Fort St. Mark[8] until the Peace of Paris (1783) when Florida was exchanged back to Spain. In 1819 Spain marked the Adams–Onís Treaty which surrendered Florida to the United States in 1821; thus the fortress was assigned a United States Army base and renamed Fort Marion, to pay tribute to American Revolutionary War legend Francis Marion. In 1942 the first name Castillo de San Marcos, was restored by an Act of Congress. The stronghold was pronounced a National Monument in 1924, and following 251 years of constant military ownership, was deactivated in 1933. The 20.48-section of land (8.29 ha) site was then swung over to the United States National Park Service.

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 various Native American tribes starting with the Seminole—including the famous war chief, Osceola, in the Second Seminole War—and members of various 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.