The history of the late-antique papacy has long fascinated historians, but studies of popes and their allies have rarely considered both Latin and Greek sources on equal terms. This thesis aims to fill this unfortunate lacuna by considering together networks of individuals aligned with papal interests from both the Roman Empire ('Byzantium') and the post-Roman West. In the process, a new interpretation of the careers of particular popes and the course of the monothelete controversy will be presented. While the seventh century is still often seen as a time when the unity of the Mediterranean world and late-antique Christendom fractured, by examining Palestinian monks, Frankish bishops, and Anglo-Saxon pilgrims together, the case is made that, from the perspectives of contemporaries, the divisions were perhaps not yet so obvious. This study begins with the friends and acquaintances of Gregory the Great, whose pontificate often looms large in histories of the early medieval West. Events in Constantinople, Alexandria, and Antioch, however, should still be integrated into narratives of the pope's actions, for specific parallels to Gregory's projects, most especially the Gregorian mission to England, can be detected in the available Greek sources. Similar connections in the seventh century are highlighted in the second chapter, which revisits papal history after Gregory's death to 649. This period remains a poorly understood and poorly documented one, but here I argue that fresh insights can be drawn from the words of the Venerable Bede and the writings of the monastic circle that gathered around the Cilician John Moschus. A revised narrative of the opening salvos of the monothelete controversy completes this analysis, for recent reinterpretations of this doctrinal debate have changed considerably our understanding of the Christological furore consuming the empire. The third and fourth chapters continue the story by venturing far beyond imperial borders. The consequences of the Lateran Synod of 649 in Visigothic Spain and Merovingian Gaul are discussed in detail first, for the imperial 'heresy' also left a tangible mark among the 'barbarians'. The hagiographical and conciliar evidence are certainly difficult to work with, but new possibilities can still be raised for how these western churches responded to pleas from Rome. The final chapter meanwhile surveys both the struggles of the anti-monothelete dissidents after the condemnation of their leaders, Pope Martin and Maximus the Confessor, and developments in Anglo-Saxon England. The careers of Wilfrid of York and Theodore of Tarsus, two men who loom large in any history of the early Anglo-Saxon church, are given particular attention. Indeed, this thesis argues that they too can be situated within imperial history, for their entanglements with Rome had exposed them to the very real consequences of papal dissent against Constantinople. Throughout this study, I argue that a transregional reading of the sources can provide more nuanced interpretations of even well-known texts. Latin histories, for example, can help to fill the gap in contemporary Greek historiography, while Greek writings are invaluable for understanding the often obscure twists and turns of papal politics. The interpretations offered here of events from Egypt to Northumbria and between Visigothic Spain and caliphal Palestine still present only a limited picture of the networks and exchanges possible in the seventh century, but the connections outlined in this thesis are, nonetheless, important additions to narratives of the end of late antiquity.