Erected in the 11C but significantly modified in subsequent centuries, this cathedral boasts a neo-Classical façade built in 1848. The mosaic paving in the chancel dating from the 12C is worthy of particular note. The church has also preserved its beautiful 15C Gothic stalls and two series of 11C frescoes. Probably painted at the same time as those at Sant'Orso, and by the same artists, the frescoes here are better preserved. The museum displays a fine collection of sacred art (13C-18C) from the Aosta valley.