Camas Cuil an t-Saimh (Bay at the Back of the Ocean), Iona.

Sometime around anno 560, St. Columba became involved in a dispute with his teacher, St. Finnian of Mainistir Mhaigh Bhile (“Monastery of the Plain of the Notable Tree”), Movilla Abbey, regarding the former’s copying of a psalter surreptitiously or without permission.  Evidently, St. Finnian either disputed Columba’s right to copy his master’s book or subsequently to retain the copy for himself.  In some convoluted way, this disagreement led to the Battle of Cúl Dreimhne in which a number of lives were lost.  After the battle, a synod of Irish clerics exiled Columba to Alba (Scotland).  Taking with him twelve disciples, St. Columba ended-up on the island of Hy (Iona), off the south-west coast of Mull, and established his apostolate there.  The account below, taken from the Annals of Inisfallen, places the Battle Cúl Dreimhne in 561 and Columba’s banishment in 563, noting that his first night in his new country was during Whitsuntide.

The copy of the psalter which provoked this trouble has been traditionally associated with the so-called Cathach (“Battler”) of St. Columba, of which more later.

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Annal AI561

AI561.1

Kl. In which the battle of Cúl Dreimne is what is to be recorded, and in which Ainmire, son of Sétna, and Ainnedid son of Fergus, and Domnall were victors.  Diarmait, however, was put to flight; and on this day Cluain Ferta Brénainn was founded at the order of an angel. [AU 558, 560, 561, 564; AU 558].

[...]

Annal AI563

AI563.1

Kl. Colum Cille in exile. His first night in Alba was during Pentecost. [AU 563].