The Collegiate church of Saint Ursus (Italian: Collegiata di Sant'Orso, French: Collégiale de Saint-Ours) is a collegiate church in Aosta, northern Italy, dedicated to Saint Ursus of Aosta.
The original church had a single hall, delimited by a semicircular apse. It was entirely rebuilt during the 9th century, during the Carolingian age. Later, bishop Anselm of Aosta further renovated the church, introducing a basilica plan with three naves with wooden trusses. These were replaced by Gothic cross vaults in the 15th century.
The church has a nave and two aisles divided by quadrangular pillars.
The vault was rebuilt in the 15th century. Fragments of a Romanesque series of paintings are preserved in good condition in the space between the current vault and the original ceiling. These portray scenes from the New Testament as well as a martyrdom. Stylistically they resemble the bright colours and strongly marked outlines of some of the frescoes at the Galliano Basilica near Cantù.[1] In the right aisles is a chapel housing the altar of St. Sebastian, also with frescoes (15th century).
The cloister has historiated capitals depicting the life of Ursus. 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.
The quadrangular-plan bell tower, dating to 989, has kept some of the lower of the original medieval structure. The present structure, in Romanesque style, dates to the 12th century and has a total height of .
The church is home to numerous missals and reliquaries, including the relics of Ursus, which rest in the crypt. It also holds the relics of Saint Gratus of Aosta.