Mamertine Prison

The Mamertine Prison, known in antiquity as the Carcer Tullianum, is the oldest known prison in Rome. It is located on the Clivo Argentario at the northeastern edge of the Roman Forum, beneath the church of San Giuseppe dei Falegnami. According to ancient tradition, the prison was founded in the seventh century BCE during the reign of King Ancus Marcius. It was intended as a secure holding place for enemies of the state who were awaiting execution, rather than as a long-term detention facility.

Ancient authors such as Livy associate the prison’s construction with Rome’s early expansion and the rise of crime within the growing city, particularly around the Aventine Hill. The threat of imprisonment in such a severe space was meant to reinforce public order and demonstrate the authority of the Roman state.

The structure consists of two chambers built into the southern slope of the Capitoline Hill. The lower chamber, known as the Tullianum, is the oldest part of the complex and dates to the Archaic period of the seventh century BCE. It is roughly semicircular in shape and lies deep below ground. Above it is the upper chamber, called the Carcer, which was added in the sixth century BCE. This room has a trapezoidal plan and is constructed from large blocks of red and yellow tuff, originally covered by a barrel vault.

The Tullianum functioned as the prison’s execution chamber. Condemned prisoners were lowered into it through a circular opening in the ceiling and held there until execution, usually by strangulation or decapitation. The historian Sallust described the space as dark, neglected, and foul-smelling, emphasizing its terrifying conditions. The name Tullianum likely derives from the Latin word tullius, meaning a spring, referring to a natural water source that flowed underneath the chamber. A drain carried this water, and the bodies of executed prisoners, into the Cloaca Maxima, Rome’s main sewer.

The prison’s location was highly symbolic. Positioned above the Forum and along the route of Roman triumphs, it played a role in public displays of victory and punishment. Captured enemy leaders were often paraded through the city during triumphal processions and then led into the Carcer to be executed. This final act marked the end of both the victorious general’s command and the defeated enemy’s life. Notable prisoners included Jugurtha, king of Numidia; Vercingetorix, leader of the Gallic resistance to Rome; and Sejanus, praetorian prefect under Emperor Tiberius.

Adjoining the prison complex were the Scalae Gemoniae, the Gemonian Steps, which joined the Capitoline Hill to the Forum. Rather than a site of execution in their own right, the steps served as a stage for the aftermath: bodies of those strangled or decapitated in the Tullianum were dragged here and left exposed to public view before being hauled off to the Tiber. Cassius Dio describes this as standard Roman custom, dragging the corpses of condemned men through the Forum and down the steps. Sejanus, the praetorian prefect executed in the Carcer under Tiberius, met this fate, his corpse dragged down the steps according to an ancient account of Tiberius’s reign. The emperor Vitellius suffered the same treatment. Like the prison itself, the display served as a visceral warning against betraying the Roman state. Visitors today can still trace the route: the modern staircase descending from the Capitoline follows the same path, laid directly over the ancient steps.

The Mamertine Prison was renovated several times during the Republican period and the early Empire, including the addition of a large travertine façade. It remained in use until at least the fourth century CE.

In Christian tradition, the prison is associated with the imprisonment of the apostles Peter and Paul before their martyrdom under Emperor Nero. Legends claim that a spring miraculously appeared in the prison, allowing Peter to baptize his fellow prisoners, and that Peter struck his head against the wall while descending into the cell, leaving an imprint in the stone. From the early Middle Ages, the site became known as the Mamertine Prison, possibly named after a nearby temple of Mars. Both chambers were converted into Christian chapels, and in the sixteenth century the church of San Giuseppe dei Falegnami was built above the ancient structure.

Today, the remains of the Mamertine Prison can still be visited beneath the church. Accessed by a narrow staircase, the dark and confined chambers preserve the stark atmosphere of one of Rome’s most feared institutions.

Bibliography

• Cadoux, T. J. (2008). The Roman Carcer and Its Adjuncts. Greece & Rome, 55(2), 202–221. http://www.jstor.org/stable/20204210
• Grout, James. “Tullianum.” University of Chicago. https://penelope.uchicago.edu/encyclopaedia_romana/romanforum/tullianum.html
• Larsen, Matthew and Mark Letteney. (2025). Spaces of Incarceration: A Typology of Prisons in Antiquity. In Ancient Mediterranean Incarceration (1st ed., pp. 45–88). University of California Press. https://doi.org/10.2307/jj.30089702.8
• Olson, Mary. (2008). “Philosophies of Imprisonment in Late Antiquity.” Constructing the Past, Vol. 9: Iss. 1, Article 7. https://digitalcommons.iwu.edu/constructing/vol9/iss1/7
• Platner, Samuel. (1929). “Carcer.” In A Topographical Dictionary of Ancient Rome (p.99-100). Retrieved from: https://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Europe/Italy/Lazio/Roma/Rome/_Texts/PLATOP*/Carcer.html
• Ruyter-Harcourt, Isadora. (2015). “A Dispatch from Rome: The Mamertine Prison.” Columbia University. https://blogs.law.columbia.edu/foucault1313/2015/10/17/the-mamertine-prison-a-dispatch-from-rome/