It was built in 1787, and was used to incarcerate wrong-doers until they could be hauled before the magistrate the following morning.
An early print of Everton Brow by Liverpool artist Herdman in 1800 shows the small round house with a conical roof in the middle of the penfold (cattle enclosure) which had been constructed to incarcerate drunks and deviants for the night.
Also going by the nicknames "Stewbum's Palace" or the "Stone Jug" in its day, there is a display about the lock-up in the Liverpool Museum.
Used primarily these days by council workmen to store their tools, the tower itself has fallen into disrepair recently but in May 1997, then-chairman Peter Johnson announced a plan to spend £15,000 on renovating what is one of Everton FC's most enduring symbols. The club's Megastore also incorporated the tower design into its commanding facade.
Note that the depiction of Rupert's Tower has changed a bit on the latest version of the Club crest — the tower has sprung a foundation visible below the girding fenceline.
In 2003, a plaque was added to the site stating its importance to Everton Football Club.