The Cathedral of Santa Maria Assunta, whose construction dates back to the 11th century, was extensively remodeled in the following centuries. Both the figurative and decorative parts of the three naves date from the late 19th c. From 1723 is the fresco in the main chapel by Francesco Porro. Of particular note is the splendid 15th-century frescoed Annunciation in the Chapel of St. John. The crypt is dedicated to St. Antonio Maria Gianelli, bishop of Bobbio from 1838 to 1846.