The Arco di Augusto (Arch of Augustus) was erected in 25 BC on the occasion of the victory of Rome over the Gallic tribe, calles the Salassi and founding the new colony.

The arch has a single vault, with a height to the keystone of 11,4 meters. Its span is a barrel vault, constituting an extension in width of a round arch, measuring 8,3 meters. The monument, which changed during centuries, consists of a single round arch framed by half-columns and surmounted by Corinthian capitals and crowned by a Doric trabeation.

The arch's modern appearance is the result of a final intervention for restoration and consolidation which occurred in 1912. 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.

Emperor Augustus name adorns not just the arch, but also the region itself: "Aosta" is a derivative of Augustus.