Slightly to the northwest of Fort Pulaski's Demilune is a tiny graveyard, in which are interred one Lt. Robert Rowan, a 25-year old Artillery officer who died at the fort on March 3, 1800; Charles Howard, infant son of Lt. Charles and Marion Sellmer, who died on June 15, 1872; and thirteen of the IMMORTAL SIX HUNDRED.

In retaliation for the Confederacy using 50 Union POW's as human shields against Federal artillery in Charleston, South Carolina in 1864, US Secretary of War Edwin M. Stanton (1814-1869) ordered that 600 captured Confederate officers be used in the same capacity against the guns of Fort Sumter, which were being fired on Federal emplacements in Charleston. After 45 days of human shieldery, the Confederate officers were moved to Fort Pulaski, where they were intentionally starved.

Thirteen of the Immortal Six Hundred died in captivity at Fort Pulaski, and they are buried here. Way to make me of all people a Confederate sympathizer, Secretary Stanton.

Sources
Wikipedia's Immortal Six Hundred page
Wikipedia's Edwin M. Stanton page