Blackgate Penitentiary was the highest level maximum security prison in the United States of America. This was primarily due to the danger of the Gotham City Rogues who did not fall insane to their own designs. Several of the deemed insane mob bosses, as Clayface or Riddler had their henchmen, their billed crew, be incarcerated in the prison. Despite it's high security, much like Arkham Asylum, the danger of the villains often made it prone to uprisings and prison breaks.
Although it was the largest prison in the Western Hemisphere, it was also renowned for being kept in worse condition than prisons as Belle Reve Penitentiary. Due to this, it was constantly combating the American Civil Liberties Union in an attempt to continue operating. Due to the small surface area of the island the prison was located, it was several stories tall and housed underground prison areas.