Mythological twin brothers played key roles in the establishment and preservation of the city of Rome. This article examines the use of one particular set of brothers, Castor and Pollux, by rival forms of government in the early fourth century ce. In his work on the representations of the Dioscuri on Roman coinage, Gricourt argues that the Dioscuri symbolise the same ideas on Maxentius’ coins as on other such imperial coinage, namely their role in maintaining the eternal order of the universe and their roles as protectors of soldiers.1 More recently, however, Marlowe and Hekster have successfully argued that Maxentius’ ideology was a counterclaim to that presented by the Tetrarchy.2 Developing this notion further with respect to Maxentius’ coinage, this article argues that, for the Tetrarchs, Castor and Pollux served as the ideal figures to symbolise the importance of concordia in the collective rule of like-minded individuals. Maxentius, however, used Castor and Pollux in connection with other symbols of the city of Rome (such as Romulus, Remus, and the she-wolf) on his coins to promote his restoration of the city of Rome (in conjunction with titles such as princeps and conservator urbis suae). The examination of this ideological conflict between Maxentius and the Tetrarchy, through their use of Castor and Pollux on their coinage, sheds light on the mutability of myth and its role in the promotion of particular aspects of mythological narratives and figures to support an individual’s own claims to power.