Across the North, 26,000 Rebels died in what was called "Yankee captivity"-six times the number of Confederate dead listed for the battle of Gettysburg, and twice that for the Southern dead of Antietam, Chickamauga, Chancellorsville, Seven Days, Shiloh, and Second Manassas combined. "If there was ever a hell on earth," one Confederate veteran remembered, "Elmira prison was that hell." New York's POW camp-nicknamed "Helmira"-was the most infamous of...