Named for King Carlos III, it was located on the left bank of the Arkansas, about 29 miles (47 km) from the mouth.

This wooden palisade fort comprised a stockade, bastions, embrasures, storehouses, barracks, officers' quarters, a powder magazine, cannons, swivel guns, and ordnance stores.

[1] Discovery of the intention of British partisans to capture Arkansas Post earlier that month prompted its construction.

Fort Carlos III was the focus of James Colbert's 1783 raid during the American Revolutionary War, during which it was a place of refuge for the local women and children.

After Captain Ignacio Delinó took control of the post in 1790, he had Fort San Estevan built about a half mile back from the river to replace the ruined structure.