Leo the Great (440-61) and Gregory the Great (590-604) earned their epithets in different ways, Leo by his intervention at the Council of Chalcedon via one momentous letter known as the Tome (Ep. 28), and Gregory by his spiritual direction, civic leadership, and his prolific publication of works in various genres, some of which were taken up by the Eastern church. This paper looks at how other late-antique popes were received in the Middle Ages, and used to promote particular agenda. It considers what kind of contribution to eastern-western Church relations was required for a pope to be remembered beyond the century in which he lived. It will be argued that successful mediation between the Roman and Byzantine churches was a prerequisite for a lasting impact on later ages. This impact can be measured by the continued popularity of their works, whether in Latin or in translations into Greek and other vernaculars. The proliferation of early and late medieval Lives of Roman bishops also testifies to their importance throughout Europe, both in Byzantium and the medieval West up to the Renaissance.