Fort Carlos III was an eighteenth-century Spanish fort at Écores Rouges in colonial Luisiana, on the Arkansas River near its mouth, and served as headquarters of Spain’s Arkansas district from 1781 to 1791. Built in 1781 as a red oak stockade after fears of a British partisan attack, it enclosed key garrison buildings and was strengthened with gates, bastions, embrasures, cannons, swivel guns, barracks, officers’ quarters, and stores. It sheltered local women and children during James Colbert’s 1783 raid. Though shaped by several commanders, the fort was ultimately destroyed not by war but by erosion and flooding, and by 1793 it had vanished beneath the water.