Carcer Tullianum (Mamertine Prison), Rome

The Mamertine Prison, originally called the Tullianum, was an ancient prison in Rome, located on the northeastern slope of the Capitoline Hill. Built in the 7th century BC, it is traditionally attributed to Ancus Marcius, Rome’s fourth king.

The origins of the name Tullianum are uncertain. Some believe it was named after the Roman kings Tullus Hostilius or Servius Tullius, while others suggest it refers to an ancient Latin word meaning water jet, as the site originally served as a cistern. The name Mamertine emerged in the medieval period, possibly referencing a nearby Temple of Mars.

As Roman law did not use imprisonment as punishment, the prison was not intended for long-term detention. Instead, it functioned primarily as a temporary holding of inmates awaiting trials or executions. As such, the site had a lower dungeon, wherein prisoners were dropped through an opening and often left in grim conditions.

The Mamertine Prison played a role in several significant historical events. In 63 BC, members of the Catiline conspiracy were executed there. Sejanus, the disgraced Praetorian Prefect, was also detained and executed at the site. Additionally, many foreign rulers captured in battle met their fate there following triumphal parades. Among them were Jugurtha, king of Numidia, and Vercingetorix, the Gaulish chieftain, both of whom died in captivity.

Rome’s policy was generally to pardon high-ranking enemies after war, using diplomacy to secure capitulation. However, figures considered especially dangerous or hated were sometimes subjected to harsh treatment, and the Mamertine Prison served as an ideal location for public humiliation before execution. The Palatine Hill, a short walk away, provided a stage for displaying conquered leaders as part of Roman propaganda.

The most prominent prisoner at the Mamertine was Saint Peter. According to Christian tradition, he was imprisoned here before his upside-down crucifixion, allegedly performing baptisms in a pre-existing spring within the jail. However, historical evidence confirming his imprisonment is limited. As for Saint Paul, whose name is also sometimes associated with this site, he was actually held elsewhere before his execution.

By late antiquity, the prison ceased operations and transitioned into a Christian Church of San Giuseppe. Today, it remains a historical and religious landmark, with an upside-down cross on its altar commemorating Saint Peter’s crucifixion.