The "fiery Columbanus" (ca. 540-615) was an Irish monk who carried Christianity to continental Europe during the Dark Ages, founding monasteries in the feudal kingdoms of what are now France and northern Italy. According to Alban Butler's Lives of the Saints, he left his mother in Ireland "grievously against her will," and in Nestor Stephen thinks of him striding across his forlorn mother's "prostrate body" in his "holy zeal" to spread the gospel.
Columbanus was famous not only for great learning and eloquence, but also for impetuous, headstrong passion. Stephen identifies with him as a man who broke away from home to go to France, and as someone who repaid his mother's love with injurious independence. In Proteus, he unflatteringly compares himself to Columbanus: "You were going to do wonders, what? Missionary to Europe after fiery Columbanus." The thought of what a poor figure he cut in France leads him to think of two other Irish missionaries to the continent, laughing at him from their heavenly vantage: "Fiacre and Scotus on their creepystools in heaven spilt from their pintpots, loudlatinlaughing: Euge! Euge!" The Latin exclamation, Thornton observes, means something like "Well done! Well done!" Mockers shout the phrase ironically several times in the Vulgate versions of Psalms and Ezekiel.
Saint Fiacre built a small monastery in France in the 7th century. Scotus, Thornton notes, could be either John Duns Scotus (a late 13th century Scholastic philosopher) or John Scotus Eriugena (a 9th century Neoplatonist theologian), both of them reputedly Irish. Though both are mentioned in Joyce's lecture "Ireland, Island of Saints and Sages" (along with Columbanus, they are the saints on whom the lecture primarily meditates), Thornton votes for Duns Scotus on the basis of a passage in Joyce's Alphabetical Notebook which served as a rough draft for the passage in Proteus. It mentions Duns Scotus in connection with Fiacre and Columbanus, and puts them on "creepy-stools in heaven."
Columbanus and Fiacre make another brief appearance in the novel in Cyclops, when Martin Cunningham's remark, "God bless all here is my prayer," triggers the appearance of many dozens of "mitred abbots and priors and guardians and monks and friars."