Castle Thunder, located between what is now 17th Street and 18th Street on northern side of E Cary Street in Richmond, Virginia, was a former tobacco warehouse, located on Tobacco Row, converted into a prison used by the Confederacy to house civilian prisoners, including captured Union spies, political prisoners and those charged with treason during the American Civil War. A large number of its inmates were sentenced to death. Even though the inmates were sometimes allowed boxes of medicine and other supplies, the prison guards had a reputation for brutality.