The Irish missionary St. Columban (ca. 543-615) traveled throughout Europe, preaching a strict, penitential version of Christianity. He founded influential monasteries in France, Switzerland, and Italy.

As a young student, Columban was so impressed by the dedicated Irish monks who introduced him to religion and literature that he decided to join their ranks. He entered a monastery at Bangor, County Down, not far from his home, and placed himself under the spiritual guidance of its founder, Comgall. For some 30 years he lived quietly in prayer, work, and study. Desiring greater self-sacrifice, Columban asked his abbot if he could go into voluntary exile, leaving his native Ireland to start a monastery on the Continent. Twelve other monks set out with him in 590 for the land of the Franks.

They settled for a while in Burgundy at the invitation of King Childebert, founding three monasteries. So many young men were...