Dating from the end of the first and the beginning of the second century AD, it is located in the western part of the ancient city. The monument, whose cavea measures about 98 meters in diameter, is built in concrete work with facing blocks of limestone and brick. The bleachers and the frons scenae were covered in marble, as well as marble slabs and stucco, still partially preserved, decorated the Aulae, the two large rooms that, through corridors (parodoi), enter the orchestra. The cavea, with a semicircular plan, is built on substructures and has three orders: Tuscanic, Ionic and Corinthian. Of these, only the lower order, consisting of twenty-five arches on pillars with semicolumns tuscaniche.

The arches of the cavea, with wide finished frame, presented as keystones reliefs configured, represented by busts in the lower order and, most likely, by masks in the upper orders. Some of these masks have been reused in buildings in the Old Town, where they are still visible. The cavea ended at the top with a gallery, in which niches opened.