[1] Managed by the United States Army, the Gratiot Military Prison housed Confederate prisoners of war (POW), sympathizers, guerrillas, spies, and federal soldiers accused of crimes.

It is well known for being the site of a daring breakout in the last days of the American Civil War.

The prison building was previously a medical school named McDowell's College, which was confiscated by the Army and converted to a prison in December 1861.

It was located at the corner of Gratiot and 8th Streets in St. Louis, and demolished in 1878.

The location is now the site of the Nestlé Purina PetCare corporate headquarters.