"The Castillo de San Marcos" (in Spanish) or "St. Mark's Castle" is the oldest masonry fort in the continental United States, located on the western shore of Matanzas Bay in St. Augustine, Florida.
The construction began in 1672, 107 years after the city was founded by Spanish Admiral and Conquistador Pedro Menéndez de Avilés when Florida was a part of the Spanish Empire.
It was designed by the Spanish engineer Ignacio Daza.
Following a raid by the English privateer Robert Searles in 1668 that severely damaged the pre-existing wooden fort and burned most of St. Augustine, Governor Francisco de la Guerra y de la Vega ordered the construction of the fort.
Manuel de Cendoya, Guerra's successor, supervised the administration of the construction from 1671 to 1672, when the first coquina stones were set.
The current fortress's main structure was started in 1695, although over the ages, it underwent numerous adjustments and renovations.
The fort, which was partially constructed by people of color that were slaves held by the Spanish, later served as one of the initial points of entry for fugitive slaves from British North America into Spanish Florida, where the colonial authorities emancipated them.
The first free people of color colony in the future United States was established as a result soon- Fort Mose, formed just north of St Augustine.
The fort was renamed Fort St. Mark when Britain took possession of Florida in 1763 as a result of the Treaty of Paris, and St. Augustine was made the capital of British East Florida. After Florida was returned to Spain in 1783 as a result of the Peace of Paris, the fort's former name was restored.
The fort was renamed Fort Marion in honor of Francis Marion, an American Revolutionary War hero when Spain signed the Adams-Ons Treaty in 1819, which gave Florida to the United States in 1821.
After 251 years of uninterrupted military control, the fort was designated a National Monument in 1924 and deactivated in 1933. The United States National Park Service afterward received ownership of the 20.48-acre land.
Castillo de San Marcos was once again used as the official name in 1942 due to a congressional act.
Castillo de San Marcos was twice besieged and repeatedly attacked by English colonial forces under the command of the governors of the Carolina Colony in 1702 and Georgia in 1740, accordingly, but it was never captured by force.
However, the fort has been controlled by four different governments five times, all peacefully: Spain from 1695 to 1763 and from 1783 to 1821; the Kingdom of Great Britain from 1763 to 1783; and the United States of America from 1821 until now.
The fort was used as a military jail under the US administration to house prisoners from Native American tribes, beginning with the Seminoles, who included Osceola, a famous war chief in the Second Seminole War, and western tribes like Geronimo's band of Chiricahua Apache.
The Native American art genre known as Ledger Art developed at the fort during the captivity of Plains tribes members such as Howling Wolf of the southern Cheyenne.
The Castillo was given to the National Park Service in 1933, and it has been a popular tourist destination ever since.
(Source: Castillo de San Marcos/ Wikipedia)