Dating back to the second half of the third century BC, it was incorporated in 1540 in the outer walls of the Rocca Paolina. Built in travertine marble, it has a round arch framed by pilasters with capitals in central rosette surmounted by a balustrade divided by four pillars in the Italian-Corinthian style from which protrude five sculptures: the center dominates the scene Jupiter between the Dioscuri, flanked by their horses at the ends. Another two heads, perhaps tutelary deities of the inputs are located in the triangles between the arch and the pilasters.