In late antiquity Roman emperors and popes oversaw projects of mind and material that gradually transformed classical Rome into Christian Rome. This book argues for the centrality of the cult of the martyrs in a metamorphosis that now stands as the most significant divide in Rome’s three-millennia-long history. Drawing on a wide range of evidence it demonstrates how shrines and churches dedicated to the Roman martyrs—founded, expanded, and embellished by emperors and popes—served as nodes around which Roman religious and civic identity were reimagined. Reimagining Rome also reveals underlying continuities that elide the religious practices and beliefs of early imperial Roman “paganism” and the Christian mentalité of the late ancient city, exposing the cognitive bedrock that supported both the city full of gods and the city of saints. My project, then, is a book about continuity as well as change and a contribution to the history of religion writ large.