the handover to Britain, and many British citizens stayed after it was returned to Spain. Many border problems arose between Spanish Florida and the new United States. Spain 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, which was transferred in 1821. First United States period Upon receiving the fort from Spain, the Americans changed its name to Fort Marion. It was named to honor General Francis Marion, an American Revolutionary War hero nicknamed "The Swamp Fox." Structurally, the Americans made few changes to the fort during this time. Many storerooms were converted to prison cells on account of their heavy doors and barred windows. Also, part of the moat was filled in and transformed into an artillery battery as part of the American coastal defense system. The original Spanish seawall was dismantled to ground level and a new seawall constructed immediately adjacent to the seaward side of the original. At this time a hotshot furnace was also built in the filled-in section of the moat behind the newly built water battery. Cannonballs were heated in the furnace to fire at wooden enemy ships. In October 1837, during the Second Seminole War, Seminole chief Osceola was taken prisoner by the Americans while attending a peace conference near Fort Peyton under a flag of truce. He was imprisoned in Fort Marion along with his followers, including Uchee Billy, King Philip and his son Coacoochee (Wild Cat), and then transported to Fort Moultrie on Sullivan's Island in Charleston's harbor. Uchee Billy was captured on September 10, 1837, and he died at the fort on November 29. His skull was kept as a curio by Dr. Frederick Weedon. The doctor also decapitated Osceola after his death in Fort Moultrie and kept the head in preservative. On November 19, 1837, Coacoochee and nineteen other Seminole, including two women, escaped from Fort Marion. 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