Caption: Fort Sumter – The Casemates: Hoisting a Gun.
Source: Illustration from Harper's Weekly, January 26, 1861, page 60.
In military architecture, a casemate, or casement, is a fortified chamber fitted with an embrasure, an opening in the wall from which guns are fired. Fort Sumter was designed with three levels of enclosed casemates, though the second level was unused at the time of the Battle of Fort Sumter.