Peter's Rock in Mohammed's Flood, from St. Gregory the Great to St. Leo III

"Peter's Rock in Mohammed's Flood" by Thomas W. Allies is a detailed, late 19th-century historical study forming part of a broader series that explores the early Christian Church's development between the eras of St. Gregory the Great and St. Leo III. It centers on the Christian faith's battle to maintain unity and authority at a time of political chaos and religious differences, especially concerning the Byzantine Empire and Islam's beginnings. Allies starts by explaining the importance of studying church history as a connected story showing divine guidance, stressing how vital unity is for the church and how dangerous doctrinal arguments can be to Christian teachings. He prepares readers to explore the interactions between popes and rulers, along with the difficulties presented by competing belief systems, like the burgeoning Islamic faith, planning to offer a full picture of how the early church handled governance, faith, and its changing relationship with worldly powers during a significant period.