Book excerpt: 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.