The original fort is a bastioned rectangle with walls of earthen ramparts faced with cedar, covering vaulted brick tunnels that contain artillery ports. The design was based on fortifications developed by Sebastian Vauban, a 17th-century French military engineer, and modified by Dennis Hart Mahan. Artillery emplacements are atop the walls, designed for cannons mounted to fire over the parapet, although there is no indication that artillery intended for the fort was ever installed. There is a dry moat surrounding the fort, and a demilune facing the river.