This book examines the two generations that spanned the collapse of the Republic and the Augustan period to understand how the concept of pax Romana, as a central ideology of Roman imperialism, evolved. The author argues for the integral nature of pax in understanding the changing dynamics of the Roman state through civil war to the creation of a new political system and world-rule. The period of the late Republic to the early Principate involved changes in the notion of imperialism. This is the story of how peace acquired a central role within imperial discourse over the course of the collapse of the Republican framework to become deployed in the legitimization of the Augustan regime. It is an examination of the movement from the debates over the content of the concept, in the dying Republic, to the creation of an authorized version controlled by the princeps, through an examination of a series of conceptions about peace, culminating with the pax augusta as the first crystallization of an imperial concept of peace. Just as there existed not one but a series of ideas concerning Roman imperialism, so too were there numerous different meanings, applications, and contexts within which Romans talked about ‘peace’. Examining these different nuances allows us insight into the ways they understood power dynamics, and how these were contingent on the political structures of the day. Roman discourses on peace were part of the wider discussion on the way in which Rome conceptualized her Empire and ideas of imperialism.