Near the gallery, along the ancient Via Salaria, are the monumental catacombs of Priscilla. One enters the site through the convent of the Benedictine Sisters of Priscilla, right in front of Villa Ada. The convent takes its name from the noblewoman who donated the land, a relative of the Acilii senatorial family.

The area is mostly tufa rock, and was carved out between the 2nd and 5th centuries AD. Extending over thirteen kilometers, the underground tunnels are thirty-five meters deep and divided into three levels, and contain about forty thousand burials. After it was abandoned in the 5th century, the catacombs were forgotten for ages, later plundered during the barbarian invasions, and only rediscovered in recent centuries.

The figure of Saint Sylvester is very important. In the 4th century, he had a basilica built right above the catacombs, whose remains were found in 1890. In 1906, following the ancient architectural structures, and to protect the site, renovation work was done involving the construction of a new ceiling, thereby creating a new basilica modeled on the previous one.