Gratiot Street Prison. Oil on canvas, painting by Martin Stadler, ca. 1864. Located at the corner of Gratiot and 8th Streets in St. Louis, the Gratiot Street Prison was the largest war prison in Missouri during the Civil War. Run by the Union Army, it was unique because it housed not only Confederate prisoners-of-war, but also guerrillas, spies and confederate sympathizers. It was demolished in 1878. The location is now the site of Nestle Purina Headquarters. Missouri History Museum