The Collegiata di Sant'Orso (Collegiate church of Saint Ursus) is dedicated to Saint Ursus of Aosta. The original church - dating back to the 5th century - had a single hall. It was entirely rebuilt in the 11th century, during the Carolingian age. Later the church was further renovated into a basilica plan with three naves with wooden trusses. These were replaced by Gothic cross vaults in the 15th century.

The church has a quite simple interior with 11th century Ottonial frescoes and a wooden choir. It is also home to numerous missals and reliquaries, including the relics of Saint Ursus, which rest in the crypt.

The Romanesque cloister (PiP3) is another religious building in the Saint Ursus complex. Its construction dates back to the 12th century. The cloister has historiated capitals (PiP4), decorated with fantastic beasts, biblical events and scenes from the life of Saint Ursus himself. 37 of the 42 original capital remains: they were originally in white marble, though now they mostly appear in dark gray color after being washed with ash paint.

Opposite the entrance of the collegiate church stands the imposing bell tower (PiP5), 46 meters tall. Originally it was a defense tower dating back to the end of the 10th century. The present structure, in Romanesque style, dates to the 12th century