A granite replica of the original prison wall stands near the corner of Broadway and Williams Street, marking the site of the Alton Military Prison — originally Illinois's first state penitentiary, built in 1833 and converted to hold Confederate prisoners during the Civil War. At its peak the prison held over 1,700 men in a facility built for far fewer, and conditions were terrible.
The smallpox epidemic of 1863-64 killed hundreds and was so severe that an island in the Mississippi was used as a quarantine zone and burial ground. The original prison was demolished after the war; the replica wall, incorporating original stonework, explains the history through interpretive panels. It is a sobering stop for anyone interested in the Civil War.