This book examines the dynastic context for Constantius II's reign as a member of the Constantinian family, first as a joint ruler with his brothers and then from 350 AD as sole Augustus. The following chapters investigate the involvement of Constantius in the imperial, administrative, legal, religious, and cultural life of the Roman empire in the fourth century AD. Constantius' handling of various threats to Roman hegemony such as the ambitions of the neighbouring Sasanian empire, and his relationships with Gallus and with Julian are explored. The book's analysis is guided by the epigraphic, iconographic, literary and legal evidence of the Roman and Byzantine periods but it is not a conventional imperial 'biography'. Rather, it examines the figure of Constantius in light of the numerous historiographical issues surrounding his memorialisation in the historical and literary sources, for instance as 'Arian' tyrant or as internecine murderer. The over-arching aim is to investigate power in the post-Constantine period, and the way in which imperial and episcopal networks related to one another with the ambition of participating in the exercise of power.