Piracy holds a special place within the field of international law because of the universal jurisdiction that applies. This article reconsiders the role of piracy in the development of universal jurisdiction. While usually a connection is established between Cicero’s ‘enemy of all’ and modern conceptions of pirates, it is argued that ‘enemy of the human species’ or ‘enemy of humanity’ is a medieval creation, used by Bartolus, which must be understood in the wake of the Renaissance of the twelfth century and the increased interest for the study of Roman Law. The criminalization of the pirate in the late Middle Ages must be understood not only as a consequence of royal power claiming a monopoly of violence at sea. Both the Italian city-states and the Hanse may have preceded royal power in criminalizing pirates. All the while, political motives in doing so were never absent.