It was originally built at the end of the 1st century BC to record the renewed alliance between Emperor Augustus and Marcus Julius Cottius, a celto-ligurian ruler, made king and Roman prefect of the Cottian Alps.
The arch has a unique arcade, in which the archivolt is supported by pilasters. The entablature rests on four Corinthian columns placed at the extremities of each corner, such that a quarter of each drum is embedded in the monument. The lowest architrave is composed of three bands of which the lowest band is thicker than the middle band, and this in turn is thicker than the top band. Above the architrave, a frieze composed of a bass relief stretches around all four sides. Above that is the cornice which has twenty-two corbels on each face and twelve on each side of the arch. The corbels’ panels are decorated with roses. On tob of that rests the attic, which displays an inscription on both faces.