The three vaulted arch composed the western gate of the city, at the beginning of the Decumanus Maximus and the end of the road coming from Lambaesis.

Above the lateral arches on both sides are deep rectangular niches, which are flanked by aediculae with smooth-stemmed Corinthian columns of coloured marble on shelves.

The whole assemblage of each lateral arch and niche was framed by two red Corinthian columns, detached from the walls and supported by pedestals.

The entablature that runs across the wall above the lateral arches protrudes above the columns, and a curvilinear pediment rests on it in turn.

This includes a statue of the gods Mars and one of Concordia erected under Emperor Septimius Severus by Lucius Licinius Optatianus, on the occasion of his election as flamen-for-life of the colonia.