Mark’s Castle”) is the oldest masonry fort in the continental United States; it is located on the western shore of Matanzas Bay in St. Augustine, Florida.

Owing to its strategic cannon placement and star-shaped design, the fort was never breached or taken by force throughout its various stages of sovereign ownership.

This quickly led to the first free Black settlement in the future United States (Fort Mose, formed just north of St Augustine).

[13][14] Ownership of the Castillo was transferred to the National Park Service in 1933, and, along with the nearby St. Augustine Historic District, has been a popular tourist destination ever since.

[15] The European city of St. Augustine was founded by the admiral Pedro Menéndez de Avilés for the Spanish Crown in 1565 on the site of a former Native American village called Seloy.

[16] The need for fortifications was recognized after it was attacked by Sir Francis Drake and his fleet of 22 ships in 1586, and over the next 80 years, a succession of nine wooden forts were built in various locations along the coastline.

After an attack in 1668 by the English pirate Robert Searle, however, during which the town of St. Augustine was burned to the ground, wooden forts were deemed inadequate, and Mariana, Queen Regent of Spain, approved the construction of a masonry fortification to protect the city.

Native Americans from Spain's nearby missions did most of the labor, with additional skilled workers brought in from Havana, Cuba.

Also, the artificial mound of the glacis in front of the walls helped to protect them from direct cannon fire attempting to breach them in a siege.

Immediately surrounding the fort was a moat which was usually kept dry, but that could be flooded with seawater to a depth of about one foot (30 cm) in case of attack by land.

[19] Slaves from the Carolina colony began escaping to St Augustine in 1687, where the Spanish agreed to free (and employ) them if they converted to Catholicism.

When an English major from Carolina attempted to retrieve escapees in 1688, the Spanish Governor Diego de Quiroga refused.

[13][14] In 1702, English colonial forces under the command of Carolina Governor James Moore Sr. embarked on an expedition to capture St. Augustine early in Queen Anne's War.

[25] The English decided to burn their ships to prevent them from falling under Spanish control, and then marched overland back to Carolina.

[27] Beginning in 1738, under the supervision of Spanish engineer Pedro Ruiz de Olano, the interior of the fort was redesigned and rebuilt.

In 1733, the British merchantmen Rebecca, commanded by Captain Robert Jenkins, was seized in the Caribbean by the Spanish coast guard.

[28] After British Admiral Edward Vernon won a significant victory at Portobelo, General James Oglethorpe, the founder of Georgia, was quick to imitate him in North America.

In order to protect the city from future blockades and sieges, the Spanish built Fort Matanzas to guard the river, which could be used as a rear entrance to avoid St. Augustine's primary defense system.

As a provision of the Treaty of Paris (1763) after the Seven Years' War, Britain gained all of Spanish Florida in exchange for returning Havana and Manila to Spain.

Several revolutionary fighters who had been captured in Charleston were held there when it was taken by the British, including three Founding Fathers; Thomas Heyward Jr., Arthur Middleton, and Edward Rutledge.

Bernardo de Gálvez, governor of Spanish Louisiana, attacked several British-held cities in West Florida, capturing all of them.

Coacoochee, known for fabricating entertaining stories, later said that only he and his friend Talmus Hadjo had escaped - by squeezing through the eight-inch (203 mm) opening of the embrasure located high in their cell and sliding down a makeshift rope into the dry moat.

[40] However the Seminole escaped, they made their way to their band's encampment at the headwaters of the Tomoka River, about forty miles south of St. Augustine.

The Confederate forces left the city the previous evening in anticipation of the arrival of the Union fleet under the command of Commodore Dupont.

[47] The fort was taken back by Union forces on March 11, 1862, when the USS Wabash entered the bay, finding the city evacuated by Confederate troops.

Pratt recruited volunteers to teach the Indian prisoners English, the Christian religion, and elements of American culture.

[51] Encouraged by the men's progress in education, residents and visitors to St. Augustine raised funds for scholarships to support nearly 20 of the former prisoners in college after they were released from Ft. Marion.

Seventeen men attended the Hampton Institute, a historically black college established in 1868 for freedmen by the American Missionary Association.

In 1964 the Castillo figured in the civil rights movement, when the "Freedom Tree" on the fort green became a gathering place for demonstrators who were not welcome across the street on what was state or private property in the age of segregation.

The demonstrations in St. Augustine, led by Robert Hayling, Hosea Williams, and Martin Luther King played an important role in bringing about passage of the landmark Civil Rights Act of 1964, one of the two great legislative accomplishments of the movement.