The ecclesiastical structure of the Roman Empire survived the movements and invasions in the west mostly intact, but the papacy was little regarded, and few of the western bishops looked to the bishop of Rome for religious or political leadership. Many of the popes prior to 750 were more concerned with Byzantine affairs and eastern theological controversies. The register, or archived copies of the letters, of Pope Gregory the Great (pope 590–604) survived, and of those more than 850 letters, the vast majority were concerned with affairs in Italy or Constantinople. The only part of Western Europe where the papacy had influence was Britain, where Gregory had sent the Gregorian mission in 597 to convert the Anglo-Saxons to Christianity. Irish missionaries were most active in Western Europe between the 5th and the 7th centuries, going first to England and Scotland and then on to the continent. Under such monks as Columba (d. 597) and Columbanus (d. 615), they founded monasteries, taught in Latin and Greek, and authored secular and religious works.