Together with Arco d'Augusto and the Ponte di Tiberio, this completes the triad of the city's main monuments dating from Roman times. Built under Hadrian in the 2nd century AD, as demonstrated by the discovery of a coin bearing the effigy of the Emperor in some masonry, it was uncovered following excavations in 1843-44, which were followed by the more important ones of 1926 and 1935. The construction of the Amphitheatre by the emperor Hadrian in the 2nd century AD is an example of the panem et circenses strategy, or the quest for the widest of public approval and the lightening of social tension by affording the people moments of collective distraction. The remains of this grand building, which played host to the ludi gladiatori, are the most important remains in the whole Region.
The amphitheatre stood on the outskirts of the town, close to the harbour and well served by roads to facilitate the arrival of spectators who came from all over the territory.
The brick structure is elliptical in shape, with its main axis measuring 118 m and the smaller one 88 m; it consisted of four concentric rings with an overall thickness of 21,80 m. The size of the elliptical arena (73,76 m and 44,52 m) made it similar to that of the Coliseum. It was 16-17 m high and its external portico had 60 arches; two are still visible, incorporated into the walls when the city gave itself a new ring of defences against the Barbarian invasions. In the Middle Ages, it was used as allotments and in the 17th century as a lazaretto. It suffered the most serious damage during WWII. Of the great complex, which could originally accomodate up to 12,000 spectators, you can still see the two arches of the esternal portico and part of the arena and the cavea.