This thesis is a study of civic patriotism in the fourth-century Roman Empire in the East. Civic patriotism is often viewed as dead or irrelevant in late Antiquity. This thesis argues that civic patriotic language remained a powerful force, being endorsed, adapted and contested by a variety of elite thinkers, three of whom this thesis studies in detail. The thesis employs the methodology of a 'language of politics' to model this process of adaption, redefinition and contestation. In particular, this thesis demonstrates that Julian and his Christian contemporaries addressed similar theological and political concerns and were part of the same debates - though providing different answers. At times, Julian's position on civic issues was closer to either Basil or Gregory than either of the two Christians were to each other. Religious allegiance thus did not entirely determine the intellectual positions even of committed late-antique religious reformers. Structurally, this thesis examines civic patriotism from three angles: a secular political language, a foil for religious reformers, and a way of linking local belonging and religious allegiance. Firstly, elites adapted the language of civic patriotism to the new political circumstances of the expanded late Roman state. They refashioned service to the patris as participating in elite networks and promoting local men to government office, advertised in literary culture through letters, poems and panegyrics. This effort was cross-confessional. Julian's enthusiasm for civic patriotic language, rather than an anachronism that, reflected mainstream fourth-century political culture. Secondly, however, ascetic and universalist ideas springing from contemporary philosophy offered significant challenges to the place of civic patriotic language in elite political thought. Basil and Gregory adapted civic terminology to describe heavenly, ecclesiastical, and monastic belonging. As a result, earthly patris had to be rejected entirely. By contrast, while Julian shared some of their theological assumptions due to his theology he did not reject the patris outright. Thirdly, Basil, Julian, and Gregory attempted to combine these attitudes by elaborating a 'spiritualised' vision of civic patriotism. They claimed civic patriotism either for Christianity or for Neoplatonic paganism, redefining civic identity and rewrite elite obligations to encourage citizens to view their patriotic and religious duties as identical. This spiritualised form of patriotism had substantial later influence on the culture, politics and society of the medieval Christian world. Overall, this thesis showcases the continuing significance of civic patriotic language in late Antiquity, and the productive tensions it fostered in political thought, practical politics, and religious culture.