National Park Service
This cutaway version of Fort Sumter shows what it would have looked like on the eve of the Civil War. The fort was built to hold three tiers of guns with two casemated levels and one open parapet level. When Federal troops occupied the fort in December, 1860 the place was still a construction site "filled with building materials, guns, carriages, shot, shell, derricks, timbers, blocks and tackle, and coils of rope in great confusion." The soldiers began the work of mounting guns and bricking up embrasures against a threatened Confederate attack.
Fort Sumter National Monument