Situated at the NE corner of the Propontis, Nicomedia (modern İzmit) was a major urban centre throughout history. Since the ancient city is buried directly beneath the modern industrial Turkish one, little was known archaeologically until recently1 when a series of painted reliefs, part of a continuous marble frieze of which c.55 m in length have been uncovered, was discovered in the Çukurbağ district. They contain a remarkable combination of imperial, agonistic and mythological scenes.2 The depictions on the frieze, precious examples of tetrarchic art, shed light not only on the socio-political history of the Later Empire but also on the creation, self-identification and reception of a new tetrarchic capital.3 The marble frieze seems to have decorated an imperial complex dating to the late 3rd and early 4th c. when Nicomedia was Diocletian‘s administrative capital for the eastern Roman empire. Among the scenes on the frieze, the group of blocks representing an adventus with Diocletian and Maximian has been published in detail, and a monograph on the Diocletianic complex is under preparation. The present article will examine the mythological depictions on the frieze.