The church of San Giovanni in Fonte, built in the Lombard era and completely rebuilt in 1123, has been used for years as a baptistery for the Cathedral. Its walls have frescoes dating back to the 14th and 15th centuries. Furthermore, here you will find the most famous work of art, a 12th-century baptismal font with reliefs depicting the life of Jesus: the Annunciation, the announcement to the shepherds, the adoration of the Magi, Herod with the soldiers, the massacre of the Innocents, the flight to Egypt and the baptism of Christ.
Part of the cathedral is also the Cloister of the Canons and the Canonical Museum, which can be accessed out of St. Helena. In the cloister, the remains are belonging to the early Christian churches that occupied this place previously, while the Museum preserves sculptures, sacred furnishings, and paintings from the 1400s, 1500s, and 1600s. Finally, the Chapter Library, accessible from Piazza del Duomo, is one of the most famous and oldest ecclesiastical libraries in Europe. Here are preserved ancient parchments, illuminated books and multiple manuscripts of inestimable value, including the Institutions of Gaius and an edition of the De Civitate Dei di Sant’Agostino.