Age of Ancient Monuments by Means of Building Stone Provenance: a Case Study of the Tullianum, Rome, Italy

The construction age of the Tullianum, the oldest portion of the Carcere Mamertino (Mamertine Jail), the early Roman execution site, is not known. Identifying the provenance of the building stone used to construct the Tullianum can aid in determining the approximate age of the structure because the introduction of different types of building materials occurred at known times. The40Ar/39Ar age of the rock used to construct the Tullianum is 36±1ka, indicating that it is Lapis albanus, which crops out only on the flanks of the Alban Hills volcano approximately 20km from Rome. Based on the general belief that the introduction of Lapis albanus as a building stone did not occur before the 4th centurybc, we interpret that the Tullianum was built, or rebuilt, after this time. This age conflicts with the architectural style of the Tullianum, which matches that of ancient cisterns, believed to date to the 7th or 6th centuries bc. This younger age for the Tullianum suggests a unique history for this building, perhaps tied to ancient religious rituals.