Between the middle of the third and the end of the second century BC an e
legant arch-shaped gate was opened in the southern side of the fourth-century city walls. Two large arches, whose sides are formed of carefully squared blocks of stone, enclose an internal tunnel roofed with a barrel \b \cf1 \ATXht22 vault\b0 \cf0 \ATXht0 . On the external supporting arch are set three heads of dark stone that may represent Jupiter and the Dioscuri.\par