Built by Augustus in travertine rock, the arch of Gallieno is located at Porta Esquilina, inside the Servian Wall. A dedication to the emperor Gallieno and his wife Salonina was inscribed on the arch in 262 AD by M. Aurelius Victor, a common citizen. Flanked by angular Corinthian pilasters, the slightly squared arch was originally intended to have three barrel vaults. In the Middle Ages, two keys from the city of Viterbo were hung on the arch as a reminder of the city’s submission to Rome; they remained there until 1825.