ARENARIO. – Shortly after the discovery of the Christian underground cemeteries on the Via Salaria in the spring of 1578, the *Sanctorum Martyrum Abundii presbyteri, Abundantii diaconi, Marciani Ioannis et filii eius Passio* (Rome 1578) was published, containing a list of texts that referred to the catacombs by the name of *arenarii*. All the early illustrators of subterranean Rome, with the exception of Bosio, held that the catacombs were former sand quarries used by Christians. One of the most frequently cited pieces of evidence was a passage from the *Passio sancti Sebastiani*, which recounted how the martyrs Marcus and Marcellianus were buried “in loco qui dicitur ad arenas, quia cryptae arenarum illic erant, ex quibus urbis moenia struebantur.”
The theory was opposed by Fr. Marchi, who, through observation of the rock formations composing the Roman subsoil, became convinced that the catacombs had been excavated solely by Christians, not for the purpose of extracting building materials, but exclusively as burial places. Indeed, parts of earlier *arenarii* used for Christian burials are found only exceptionally in Rome, as in the catacombs of Priscilla, Domitilla, and Commodilla (B. Bagatti, *Il cimitero di Commodilla*, Vatican City 1936, p. 35, fig. 22). The galleries of *arenarii* were much wider, vaulted, with rounded walls, typically measuring about 2.20 m in width by 2.30 m in height, whereas the galleries excavated by Christians are much narrower and have vertical walls.
Outside Rome, the cemetery known as S. Gennaro dei Poveri at Capodimonte in Naples and that called S. Maria della Stella at Albano also make use of galleries already excavated for the extraction of building materials.