Legend has it that Columba's exile was an act of penance, and that he deliberately chose an island out of sight of his beloved Ireland. During a visit to Moville, Columba is said to have secretly copied a book of psalms. When Finnian discovered this, he insisted on having the copy. Columba refused to hand it over, and their dispute was referred to the high king, Diarmuid, who ruled: "To every cow her calf, and to every book its copy". Columba already resented Diarmuid for slaying a youth to whom the saint had given sanctuary and he persuaded his kinsmen to wage war. Diarmuid was defeated at Cuildreimhne, Co. Sligo and Columba was blamed for the hundreds of dead. When a synod called on him to make amends by converting an equal number of pagans, he opted to work among the Picts of Scotland.Columba of Iona
Happily corrected! Thank you!
(Alas, my memory fades!)