Built in 1778 on the island's highest ground, Redoubt 7 blocked the western land approach to the Great Chain's anchor on Constitution Island. In constructing the redoubt's stone rampart, the Army used a large granite outcropping as part of the southwest wall. On this rampart was an earthen parapet held in place by timber or fascines. About 80 infantrymen, unsupported by cannon, were expected to defend Redoubt 7.
In 1782, with the war drawing to a close, Henry Knox, the West Point commandant, wrote George Washington that "the West redoubt on Constitution Island has a roof put upon it, and is otherways prepared as a temporary deposite of powder." Its use as a magazine continued until 1797, when all of the powder was transferred to West Point.