The complex of Sant'orso, dedicated to St. Ursu Dutchess of Aosta's apartments, is one of the major attractions of the Aosta valley and one of the most interesting religious complexes in the Alps, consisting of the churches of Saint Peter and Sant'orso, wonderful freestanding bell tower, superior of the cloister and a small monastery in the Renaissance style.

In ancient times in place of the complex of Sant'orso was an extensive urban necropolis, which in the 5th century was built the early Christian Church. The original building of the Church of St. Orso consisted of one room, bounded by a semicircular apse. And in the 9th century, during the reign of the Carolingian dynasty, it was completely rebuilt. Later on the initiative of the local Bishop Anselm in the Church was held she reconstruction – this time she was built on the Basilica plan with three naves with wooden trusses. The latest in the 15th century was replaced by a Gothic groin vaults. To Gothic same period include choirs and mosaics.

Today in the Church of Sant'orso houses many Masalov – liturgical books and reliquaries, including the relics of St URSA, whose remains rest in the crypt, and the relics of the Holy Gratus Osciskigo. Particularly noteworthy is the cloister of the Church is decorated with figures of people and animals capitals depicting scenes from the life of URSA Osciskigo, - it is called "marble masterpiece." The cloister consists of 37 marble columns, however, its Northern part, in the 18th century was demolished.

44-meter high bell tower of the complex, built in the 989th year, kept part of the original medieval structure, although its present Romanesque appearance she found in the 12th century. Inside the Church, in the space between the current set and the original ceiling, fragments of Romanesque murals depicting scenes from the New Testament.