Arkham Island was the successor to Arkham Asylum. Built much like Blackgate Penitentiary and the Metropolis Armory Ward, Arkham Island was situated on a location from which villains would be unable to escape. To add to this measure, it's designs were made by the Riddler himself. While the prison could not be broken out of, it could also not be broken into. The one flaw in the system was that prison breaks were still possible, the prisoners just could not leave. The one notable prison break that occured was when Julian Day, the Calendarman, used his goons to take control of the prison and demand the man who ruined his family.