Fort San Carlos, known later as Fort Carlos, was the name given to a series of at least two simple stockade forts built during the Spanish ownership of Arkansas Post (1763-1789) with the purpose of protecting the trading post from attack. Both incarnations of the fort were the focus of the post, containing the commander's house, barrack, commissary's apartment, provision storage, and powder magazines. The forts were named for Charles (Carlos) III, who was King of Spain in the latter half of the 18th century during which Spain possessed the post. The forts were located about 10 miles from the mouth of the Arkansas River, and at a second location about 35 miles upriver, on the north bank. The remains of all the Spanish forts are now inundated by the river, due to erosion of riverbanks, chang