You are standing inside the Interior Fort, facing its north wall - the most imposing earthwork on Maryland Heights. This nine-foot-high parapet and accompanying ditch defended the crest from attack from the north. The five embrasures which cut through this wall served as artillery positions for howitzer guns, and later, 30-pounder Parrott Rifles.
A Union recommendation that "all plateaus or gentle slopes between the crest and Harpers Ferry be held" suggests the purpose and origin of the Interior Fort. As a rectangular earthwork, its defensive position included part of the mountain's crest and a narrow plateau just below. Built during the winter of 1862-1863, it borders the Exterior Fort on the west and encompasses the Stone Fort within its southeast corner.
Archaeological surveys recorded thirteen powder magazines on Maryland Heights, three within this fort. Used to store gun powder and shells, these 30'x20' rectangular excavations were dug to a depth of eight feet, supported by a heavy timber superstructure and covered with earth and sod.
Working around a powder magazine could be hazardous, especially to the untrained but enthusiastic soldier, as revealed in this passge by Joseph Barry, a local citizen:
"A company of them [the Hundred-Day Men from Ohio] were preparing dinner and, not having anything convenient on which to build their fire, they procured from an ammunition wagon several large shells on which they piled their wood which was soon ablaze. 'Round the fire they all squatted... Soon a terrific explosion shook the surrounding hills, sending all the culinary utensils flying over the tree tops and, unfortunately, killing or wounding nearly every man of the group."