\When prisoner exchanges with the South stopped in 1863, Northern prison camps like Point Lookout Prison in Maryland became very overcrowded. On May 19, 1864, Camp Rathbun (Camp No. 3), located on West Water Street in Elmira, was ordered to be changed from a training camp to a prisoner-of-war camp to take in the extra prisoners. By that time, two of the training camps had already closed and the remaining two were mostly empty. Over the course of the next two months, a 12 foot tall stockade fence, additional barracks and a hospital were built to accommodate the arrival of Confederate prisoners.