Constructed from conglomerate, the arch has a single vault, with a height to the keystone of 11.4 metres (37 ft). Its span is a barrel vault, constituting an extension in width of a round arch.
In the monument, various styles can be recognised: The ten engaged columns which decorate its facade and its sides culminate in Corinthian capitals, while the entablature, adorned with metopes and triglyphs, is of the Doric order.
In the Medieval period, it came to be called the Saint-Voût (French for "Holy Arch") from an image of Jesus which was located in the same place.
During the 12th century, the arch contained the home of a local noble family and in 1318 a small fortification was built inside it, designed for a corps of crossbowmen. In 1716, because of the numerous leaks that were compromising the integrity of the monument, the attic that previously crowned the arch was replaced with a slate roof.
The arch's modern appearance is the result of a final intervention for restoration and consolidation which occurred in 1912 under the direction of Ernesto Schiaparelli.[1]
The wooden crucifix displayed below the vault is a copy of the one which was placed there in 1449 as a votive offering against the flooding of the river Buthier, which flows a little to the east. The original crucifix is now housed in the Museum of Aosta Cathedral's Treasures.
