The arch of Gallienus was a monumental structure, originally built as a triple arched gate in the Servian Wall, during the Augustan Period, it but remained a utilitarian city gate rather than a triumphal arch. In 262 CE, the equestrian (Marcus) Aurelius Victor rededicated the arch to Emperor Gallienus and his wife, Salonina, replacing the original inscription in an effort to bolster the emperor's image during a period of crisis. This rededication led to the modern name "Arch of Gallienus", though the structure itself significantly predates his reign.

circa 20 BCE- 20 CE

The arch remains standing on the ancient Clivus Suburanus (modern Via San Vito), now partially incorporated into the adjacent church of San Vito. In antiquity, the Porta Esquilina formed part of the Esquiline Forum, which included the Macellum Liviae market complex. As these buildings fell into disuse in late antiquity, they were repurposed for religious use, a transition recorded in the Einsiedeln Itinerary.

The surviving portion of the arch (inspect) is a single travertine arch measuring 8.80 meters high, 7.30 meters wide, and 3.50 meters deep. It features Corinthian pilasters supporting an entablature with a dedicatory inscription. A 15th-century drawing suggests that the original structure included additional smaller pedestrian arches, which were later removed. Though the inscription to Gallienus remains partially visible, evidence of an earlier inscription, likely referring to his father, Emperor Valerian, suggests that the rededication erased its original dedication.

The two remaining lines are the final part of an inscription. Above them, a large empty space once held marble slabs with the rest of the text, attached using metal fixings—traces of these fixings can still be seen. The missing section likely mentioned Emperor Valerian, Gallienus' father, who was captured by the Sassanid Persians in 260 CE. The surviving inscription reads:

GALLIENO CLEMENTISSIMO PRINCIPI
CVIVS INVICTA VIRTVS SOLA PIETATE
SVPERACTA EST ET SALONINAE
SANCTISSIMAE AVGVSTAE AVRELIVS
VICTOR V[ir] E[gregius] DICATISSIMVS
NVMINI MAIESTATIQVE EORVM

To Gallienus, the most clement princeps,
whose unconquered virtus is only outdone
by his pietas, and to Salonina,
most holy Augusta, Aurelius
Victor, the excellent man, [dedicated this] in complete devotion
to their numina and majesty