Abstract
Celtic Christianity significantly contributed to the medieval Christian mission in the Christianization of Britain and Ireland. The Celtic missionary monks, particularly in the sixth century, set out in groups, traveled across Europe, and carried out the most remarkable missionary movement. The Celtic missionaries employed preaching methods that included non-Christians as well as Christians whom they saw as corrupted. This study examines the introduction of Christianity to Britain and Western Europe, as well as the religious and political developments that occurred in these regions until the seventh century. It also discusses the concept of peregrinatio, which describes the journeys of Celtic missionaries to spread the message of Christ. It analyzes this movement through the three key figures of the Celtic missionary movement: St. Columba (520-597), St. Aidan (590-651), and St. Columbanus (543-615). Finally, it highlights the similarities and differences among the names mentioned above in carrying out their missionary activities, including the materials they used, the problems they encountered, and the methods they used to achieve the missionary objective.