Plaza San Carlos, atop a bluff of the Amelia River in Old Town, is one of the most historically significant places on Amelia Island. The area was inhabited by Native Americans of St. Johns culture as early as 1000 BC, and was later used as a campsite by the Timucua. Franciscan missionaries established the mission of Santa Maria de Sena in 1602 near Plaza San Carlos, and a Spanish watch house was built on the site in 1696. In later colonial times, the spot increased in military importance because of its deep harbor, and its deliberate placement near the northern boundary of Spanish Florida. In 1763, under the terms of the treaty that ended the Seven Years War, also known as the French and Indian War, the British gained control of the entirety of Florida. A map was drawn up in 1769, showing plans for a community on Amelia Island, but the American Revolution interfered and the anticipated settlement never developed. As late as 1777 the land remained unoccupied. Spain reclaimed Florida in 1783 due to its alliance with the United States during the American Revolution. On January 1, 1811, the town of Fernandina was named in honor of King Ferdinand VII of Spain. In May, Governor Juan Jose Estrada brought Surveyor General George Clarke to plat the town in accordance with the Law of the Indies, which regulated the design and development of communities in the Spanish colonies. In 1816, the Spanish built Fort San Carlos on the bluff overlooking the Amelia River. Two blockhouses with 10 mounted guns were protected on three sides by a wooden, moon-shaped picket fence. The area that once served as a Native American campsite became the fort’s parade ground. The fort was taken numerous times by invading forces, including Scottish mercenary Gregor MacGregor and French privateer Luis Aury. Fort San Carlos was left unoccupied in 1821 after Florida became a territory of the United States. Fernandina remained centered around the plaza for three decades, until Yulee’s Florida Railroad shifted the center of town approximately one mile south. Fort San Carlos was allowed to slowly deteriorate, and in 1847 work began on nearby Fort Clinch. In 1861, Confederate troops occupied the plaza and began constructing new batteries on the site, but when the Union Army captured Fernandina in 1862, Fort San Carlos was abandoned for good. After being the site of the Government House, the land became part of the Florida Park Service in 1949. Archaeologists estimate that two-thirds of the area the fort once occupied has been lost to erosion.