In addition to housing the Etruscan-Roman and early-Christian relics found under and around the cathedral, the cathedral museum has a fine collection of 15C and 16C illuminated religious books, which came from Monte Oliveto Maggiore Abbey, as well as gold and silver ware, reliquaries and religious ornaments. The tour of the Porsenna Labyrinth, an Ancient water system, starts in the museum and ends with the Etruscan-Roman cistern (2C BC).