Castillo de San Marcos
The Castillo de San Marcos is the oldest masonry fort in the United States located in the city of St. Augustine, Florida. Construction was begun on the fort in 1672 by the Spanish when Florida was a Spanish possession. During the twenty year period of British occupation from 1763 until 1784, the fort was renamed Fort St. Mark , and after Florida became a U.S. territory in 1821 the fort was again renamed to Fort Marion, in honor of revolutionary war hero Francis Marion. In 1942 the original name of Castillo de San Marcos was restored by Congress.

The European city of St. Augustine was founded by admiral Pedro Menéndez de Avilés for the Spanish Crown in 1565 on a site of a former Native American village. Over the next one hundred years, the Spanish built nine wooden forts for the defense of the town in various locations. Following the 1668 attack of the English pirate Robert Searle, Mariana Queen Regent of Spain, approved the construction of a masonry fortification to protect the city. The Castillo is a masonry star fort made of a stone called coquina , Spanish for "little shells", made of ancient shells that have bonded together to form a type of stone similar to limestone. Workers were brought in from Havana, Cuba, to construct the fort in addition to Native American laborers. The coquina was quarried from Anastasia Island in what is today Anastasia State Park across Matanzas Bay from the Castillo, and ferried across to the construction site. Construction began on October 2, 1672 and lasted twenty-three years, being completed in 1695.

First British siege
In 1670, Charles Town (modern-day Charleston, South Carolina) was founded by the British. As it was just two days sail from St. Augustine, the British settlement spurred the Spanish in their construction of a fort. In November 1702, English forces under orders from Governor James Moore of Charles Town, set sail from Carolina in an attempt to capture the city. This was one of the events of Queen Anne's War. The English laid siege to St. Augustine. All of the city's residents, some 1,200 people, along with the fort's 300 soldiers remained protected inside the wall of the fort for the next two months during the siege. The English cannon had little effect on the walls of the fort. The coquina was very effective at absorbing the impact of the shells, allowing little damage to the walls. The siege was broken when the Spanish fleet from Havana, Cuba arrived, trapping the English forces in the bay. The English burned their ships to prevent their falling into Spanish control, and marched overland back to Carolina. As they withdrew, they set fire to St. Augustine, burning much of it to the ground.

Second period of construction
Beginning in 1738, under the supervision of Spanish engineer Pedro Ruiz de Olano, the interior of the fort was redesigned and rebuilt. Interior rooms were made deeper, and vaulted ceilings replaced the original wooden ones. The vaulted ceilings allowed for better protection from bombardments and allowed for cannon to be placed along the gun deck, not just at the corner bastions. The new ceilings required the height of the exterior wall to be increased from 26 to 33 feet.

Second British Siege
Spain and England had been rivals in Europe. Because the two countries had initiated empires in the New World, their heated rivalry continued. In 1733, an English vessel, the Rebecca, commanded by Captain Robert Jenkins, was seized in the Caribbean by the Spanish coast guard. Suspecting that the English had been trading illegally with Spanish colonies (which was forbidden by both Spain and England), the Spanish searched the ship. A fight broke out between the Spanish and British sailors. In the skirmish, Jenkins had his ear cut off by a Spanish officer, who picked it up and said "Take this to your king and tell him that if he were here I would serve him in the same manner!" When Jenkins reported the incident to British authorities, they used it as a catalyst to declare war on Spain in 1739. The war was called the War of Jenkins Ear. After English Admiral Vernon scored a huge victory at Portobelo, General James Oglethorpe, the founder of Georgia, was quick to imitate him in North America. In June of 1740, Oglethorpe and an English fleet of seven ships appeared off St. Augustine. As in the 1702 siege, 300 hundred soldiers and 1300 residents found refuge within the Castillo's walls. For 27 days the English bombarded the Castillo and St. Augustine. Realizing his cannon were not affecting the Castillo's walls, Oglethorpe decided to starve the people of St. Augustine by blockading the inlet at he Matanzas River and all roads into St. Augustine. No supplies could reach the city. With morale and supplies low for his own forces, Oglethorpe had to retreat. The Castillo de San Marcos had survived again. To protect the Castle from future blockades and siege the Fort Matanzas was built.

British occupation
In 1763, the British managed to take control of the Castillo but not by force. As a provision of the Treaty of Paris (1763) after the Seven Years War, Britain gained all of Florida in exchange for returning Havana and Manila to Spain. On July 21, 1763, the Spanish governor turned the Castillo over to the British. The British would make a few changes to the fort, and renamed it Fort St. Mark. As Great Britain was the dominant power in North America, they were not worried about keeping the fort in top condition. This attitude prevailed until the outbreak of the American Revolution. During the war, St. Augustine became the capital of the British colony of East Florida. Improvements were begun on the fort, in keeping with its new role as a base of operations for the British in the South. The gates and walls were repaired, and several rooms had second floors added to increase the housing capacity of the fort. The Castillo saw action during the American Revolution mainly as a prison. Several revolutionary fighters were held there who had been captured in Charleston when it was taken by the British. The Spanish declared war on Britain in 1779, drawing off forces from Fort St. Mark and keeping the British occupied. Bernardo de Gálvez, governor of Spanish Louisiana, attacked several British-held cities, capturing all of them. The British never organized any major actions against the Americans from the Castillo. At the end of the war, the Second Treaty of Paris returned Florida to Spain. On July 12, 1784, Spanish troops returned to St. Augustine.

Second Spanish period
When Florida was returned to Spanish control, they found a much changed territory. Many Spaniards had left Florida after the hand over to Britain, and many British citizens stayed after the hand over back to Spain. Many border problems arose between Spanish Florida and the new United States. Spain had changed the name of the fort back to the Castillo de San Marcos, and continued to build upon the improvements that Britain had made to the fort in an effort to strengthen Spain’s hold on the territory. However, due to increased pressure from the United States and several other factors, in 1819, Spain signed the Adams-Onís Treaty, ceding Florida to the United States.

First United States period
Upon the hand over to the United States, the Americans changed the name of the Castillo to Fort Marion. Structurally, they made few changes to the fort during this time. Many storerooms were converted to prison cells, due to their heavy doors and barred windows. Also, part of the moat was transformed into a battery as part of the American coastal defense system. In October 1837, during the Second Seminole War, the Seminole chief, Osceola was taken prisoner while attending a peace conference under a flag of truce and imprisoned in the fort along with his followers. Imprisoned along with Osceola, were Uchee Billy, King Philip and his son Coacoochee (Wild Cat). Uchee Billy captured on September 10, 1937 would die at the fort two and half months later on November 29. His skull was kept by Dr. Frederick Weedon as a curio, who also decapitated Osceola's head after his death in Fort Moultrie, and kept that one in preservative. On the night of November 19, 1837 Coacoochee along with Talmus Hadjo, 16 other Seminole braves and two Seminole women escaped from Fort Marion by squeezing through the eight inch opening of the embrasure located high in their cell and sliding down a makeshift rope into the moat. They made their way to their band's encampment where the Tomoka River meet the Atlantic. Due to their treatment they vowed to continue fighting and prolonged the war for four more years. In the past Coacoochee's Cell from which he escaped was part of the official lore of the fort.

Confederate States period
In January 1861, Florida seceded from the United States in the opening months of the American Civil War. Union troops had withdrawn from the fort, leaving only one man behind as caretaker. In January 1861, Confederate troops marched on the fort. The Union soldier manning the fort refused to surrender it unless he was given a receipt for it from the Confederacy. He was given the receipt and the fort was taken by the Confederacy without a shot. Most of the artillery in the fort was sent to other forts, leaving the fort nearly defenseless.

Second United States period
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. The city leaders were willing to surrender in order to preserve the town, and the city and the fort were retaken without firing a shot. Throughout the rest of the fort's operational history, it was used as a military prison. Beginning in 1875, numerous Native American prisoners were held at the fort in the aftermath of the Indian Wars in the west. Many would die at the fort. Among the captives was Chief White Horse of the Kiowa. During this period, Benjamin Henry Pratt, a Civil War veteran, supervised the prisoners and upgraded the conditions for them. He developed ways to give the men more autonomy and attempted to organize educational and cultural programs for them. They became a center of interest to northerners vacationing in St. Augustine, who included teachers and missionaries. Pratt recruited volunteers to teach the Indian prisoners English, Christian religion, and elements of American culture. He and most US officials believed that such assimilation was needed for the Indians' survival in the changing society. The men were also encouraged to make art; they created hundreds of drawings. Some of the collection of Ledger Art by Fort Marion artists is held by the Smithsonian Institution. It may be viewed online. Encouraged by the men's progress in education, citizens raised funds to send nearly 20 of the prisoners to college after they were released from Ft. Marion. Seventeen men went to the Hampton Institute, a historically black college. Others were sponsored and educated in New York state at private colleges. Among the latter were David Pendleton Oakerhater, as he became known, who was sponsored by US Senator Pendleton and his wife. He studied and later was ordained as an Episcopal priest. He returned to the West to work as a missionary with Indian tribes. He was later recognized by the Episcopal Church as a saint. Based on his experience at Fort Marion, Pratt recommended wider education of Indian children, a cause which Senator Pendleton embraced. He sponsored a bill supporting this goal, and the US Army offered the Carlisle Barracks in central Pennsylvania as the site of the first Indian boarding school. Its programs were developed along the industrial school model of Hampton and Tuskegee Institutes, which officials thought appropriate to prepare Native Americans for what was generally rural reservation life. Through the early 20th century, the government founded 26 other Indian boarding schools, and permitted more than 450 boarding schools run by religious organizations. From 1886-1887, approximately 491 Apaches were held prisoner at Fort Marion; many were of the Chiricahua and Warm Springs Apache bands from Arizona. There were 82 men and the rest were women and children. Among the men, 14, including Chatto, had previously been paid scouts for the US Army. Among the Chiricahua were members of the notable chief Geronimo's band, including his wife. Geronimo was sent to Fort Pickens, in violation of his agreed terms of surrender. While at the fort, many of the prisoners had to camp in tents, as there was not sufficient space for them. At least 24 Apaches died as prisoners and were buried in North Beach. In 1898, over 200 deserters from the Spanish-American War were imprisoned at the fort. This marked one of the last uses of the fort as an operational base. In 1900, the fort was taken off the active duty rolls after 205 years of service under five different flags. In 1924, the fort was designated a National Monument. In 1933 it was transferred to the National Park Service from the War Department. In 1942, in honor of its Spanish heritage, Congress authorized renaming the fort as Castillo de San Marcos. As an historic property of the National Park Service, the National Monument was listed on the National Register of Historic Places (NRHP) on October 15, 1966. The National Park Service manages the Castillo together with Fort Matanzas National Monument. In 1975, the Castillo was designated an Historic Civil Engineering Landmark by the American Society of Civil Engineers. Since being transferred to the Park Service, the Castillo has become a popular tourist attraction. It occupies 2.5 acres (101,000 m²) in downtown St. Augustine, Florida.