The design called for a two-tiered casemates in a six-sided outline, with two curtain walls measuring , and the other four measuring . Corner bastions, which are large projections designed to allow defensive fire along the faces of the walls they joined, contained gunrooms, gunpowder magazines and a granite spiral staircase. Each tier of casemates contained 150 guns, and another 150 were placed on top of the fort itself. The heavy guns were mounted inside the walls in a string of open casemates, or gunrooms, facing outward toward the sea through large openings called embrasures. The parade ground contained additional powder magazines, headquarters, a hospital, officer quarters and three large barracks.
