The church of San Venanzio, built outside the city walls of Camerino in medieval times, was then included within the new walls built by Giovanni Varano in 1384.
In the crypt, the altar is constituted by the Sarcophagus of San Porfirio, from the 2nd century AD. C., Roman sarcophagus in white marble made to contain the relics of San Porfirio, martyr in 253 d. C., and decorated between the end of the 13th and the beginning of the 14th century on one side to pretend a small Gothic temple. The epigraph, which is found on the side against the wall, has been abraded and only D. M. (Dis Manibus) can be read.
Above this sarcophagus, supported by four crouching gryphons in black marble in the four corners, is the ark of San Venanzio, attributed by Venturi to a Tuscan artist, built in limestone with twisted columns under Berardo da Varano (1310-1327), which houses the urn with the relics of the martyr, made of wood covered with silver foils, decorated with graffiti depicting episodes from his life, datable between the 10th and 13th centuries. The crypt also preserves a richly decorated aedicule with a candelabra frame, perhaps the work of Rocco da Vicenza. The silver statue of the saint was cast by Bishop Francesco Vivani in 1764 and donated with six silver candelabra.