Although the Roman empire was one of the longest lasting in history, it was never ideologically conceived by its rulers or inhabitants as a territory within fixed limits. Yet Roman armies clearly reached certain points - which today we call frontiers - where they simply stopped advancing and annexing new territories. In Frontiers of the Roman Empire, Whittaker examines the Roman frontiers both in terms of what they meant to the Romans and in their military, economic, and social function. Whittaker begins by discussing the Romans' ideological vision of geographic space - demonstrating, for example, how an interest in precise boundaries of organized territories never included a desire to set limits on controls of unorganized space beyond these territories. He then describes the role of frontiers in the expanding empire, including an attempt to answer the question of why the frontiers stopped where they did. He examines the economy and society of the frontiers. Finally, he discusses the pressure hostile outsiders placed on the frontiers, and their eventual collapse. Observing that frontiers are rarely, if ever, static, Whittaker concludes that the very success of the Roman frontiers as permeable border zones sowed the seeds of their eventual destruction. As the frontiers of the late empire ceased to function, the ideological distinctions between Romans and barbarians became blurred. Yet the very permeability of the frontiers, Whittaker contends, also permitted a transformation of Roman society, breathing new life into the empire rather than causing its complete extinction.