Cathedral of Santa Maria Assunta - is the main Roman Catholic church in Aosta .  The place where the city now stretches Piazza Giovanni XXIII, was once the southern part of the Roman Forum during the existence of the colony of Augusta Pretoria .  Even after the fall of the Roman Empire and the decline of the colony, this place has not lost its primary importance in the life of citizens .  It was here, to the west of the cloister - Kriptoportika at the end of the 4th century, it was built the first Christian building of Aosta .  It was a building of impressive size with a single nave ending in an apse, the baptistery in the western part and different rooms, one of which was used as the second Baptistery .  The facade of the cathedral was located a few meters from the eastern wing Kriptoportika was actually connected to it .  The entire complex, which was later built out several rooms, for centuries been used as a residence for the bishop and the clergy, and its appearance did not undergo significant changes until the late Middle Ages .  Priceless cycle of frescoes discovered during archaeological works in the attic of the church also dates back to the 11th century - thanks to these frescoes, as well as frescoes in the church of St Orso, Aosta ottonskogo considered the center of art in Europe . 

In the second half of the 11th century, the western part of the cathedral was completely rebuilt - if it consisted of two towers and an overhanging central apse. In the 13th century two of the five original apses were demolished and in their place erected a cloister and a ring-shaped corridor around the choir. Between the 15th and 16th centuries the cathedral at the initiative of the then bishop adorned by various works of art. In the upper choir loft, decorated wooden crucifix, there are two rows of carved seats and the floor was paved with mosaics. The main Baroque altar of the Cathedral of Santa Maria Assunta is made of black marble with color highlights. Two staircases lead from the choirs down to the crypt of the 11th century, with little medieval columns.

The current facade of the cathedral is composed of two distinct parts: an atrium dates back to the 16th century, and the neo-classical pediment was built in 1848. The atrium is decorated with terracotta statues and frescoes. Near the church, on the north side, it is cloister - cloister. It was built in 1460, the year on the site of an ancient and remarkable in that it is created using different materials - stone gray "bardilo" for the pilasters, crystalline limestone and sandstone to capitals for arches and lining. In the center stands the Romanesque columns with Corinthian capitals.

In 1985, in the Cathedral Museum was opened, acquainting visitors with the local art 13-18 centuries.