Gratiot Street Prison
Run by the Union Army, it housed Confederate prisoners-of-war, confederate 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 Union Army and converted to a prison in December 1861. Its official capacity was 1,200 but at times it had 2,000 prisoners. The prison was used mostly as a transfer point for prisoners going to other Union prisons. 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 Ralston Purina headquarters.