Named for deceased Lt. Col. Thomas M. Wagner, Fort Wagner measured 250 by , and spanned an area between the Atlantic on the east and an impassable swamp on the west. Its walls, composed of sand and earth, rose above the level beach and were supported by palmetto logs and sandbags. The fort's arsenal included fourteen cannons, the largest a Columbiad that fired a 128-pound shell. A large structure capable of sheltering nearly 1,000 of the fort's 1,700-man garrison provided substantial protection against naval shelling. The fort's land face was protected by a water-filled trench, wide and deep, surrounded by buried land mines and sharpened palmetto stakes.