The Arch of Augustus stands at the eastern edge of the old Roman town, just beyond the Porta Praetoria and close to the point where the Roman bridge over the Buthier once stood. It was erected in 25 BC to mark the Roman victory over the local Salassi tribe and the foundation of Augusta Praetoria as a garrison colony for veteran soldiers. Single-span triumphal arches of this type were standard imperial propaganda — a permanent marker that this territory now belonged to Rome.
What makes the Aosta arch notable is its state of preservation and its continued position within the living city. The medieval town grew up around it, and the arch became incorporated into the urban fabric rather than being dismantled or buried. The original marble facing that would have covered the concrete core is long gone, but the proportions of the single barrel vault are still impressive, and the Corinthian pilasters on the piers give some idea of the original decoration. A medieval cross was later added to the apex, visible in photographs and in person from the road below.