It dates to the 1st century AD, though it was most likely built over a pre-existing gate from the 1st century BC. An inscription dating from emperor Gallienus' reign reports another reconstruction in 265 AD.
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The Via Postumia (which here became the decumanus maximus) passed through the gate, which was the city's main entrance and was therefore richly decorated. It also originally had an inner court, now disappeared.