Columbanus founded several monasteries in the Frankish kingdom, most notably Luxeuil in 590, spreading among the Franks a Celtic monastic rule and Celtic penitential practices for those repenting of sins. Private confession to a priest was emphasized in this practice, followed by penances levied by the priest in reparation for the sin.
Because of political difficulties with bishops and Merovingian kings, including difficulties over the date for the celebration of Easter, Columbanus moved south into Italy in about 612, where, with the help of the Lombard King Agilulf and Queen Theodelinda, he established his final and most important monastery at Bobbio (between Milan and Genoa), and died there in 615. (This monastery is in part the model for the great monastery in Umberto Eco's novel The Name of the Rose.)
He is often confused with Saint Columba.