It begins with Columba. A prince from an Irish noble family, in his youth Columba became a priest and a missionary monk, founding a number of monastic houses in Ireland before a tribal feud forced him into exile. In 563, he and twelve companions arrived by coracle on Iona, at that time part of a colony on mainland Britain occupied by fellow Scots from his part of Ireland.
For the next 34 years, Columba and his monks, from their base on Iona, pursued an active missionary outreach, of what has come to be known as Celtic Christianity, throughout the Western Isle and up into the north eastern parts of what is now Scotland. Their wooden and wattle settlement on Iona, large parts of whose boundary vallum, or earth wall and ditch, can still be seen today, came to be known through the area as a centre of learning, healing, and hospitality.Their missionary method was to go out in small groups, set up their huts in the midst of their pagan neighbours (Columba called them “colonies of heaven”), and seek to attract people to the Gospel by their way of life, their care for all, and the preaching and practise of their faith.
Columba died in 597, the same year which saw the arrival in England from Rome of Augustine, sent by the Pope to convert the pagan Angles to the Roman style of Christianity. Columba's successors, still based on Iona, carried on the work he started, extending their missionary reach to the north of England and even into continental Europe. In 664, at Whitby, a synod of the church decided that the Roman style of the faith was from then on to be the dominant one in mainland Britain. The Celtic way continued, albeit with less energy, for some time, still centred on Iona.
In 802, the settlement on Iona was laid waste by a Viking raid. Forty years later, Columba's remains were removed to Dunkeld, and the monks gradually withdrew to the safer shores of Ireland, taking with them the Book of Kells, which can still be seen today in Dublin. The centre of Scottish Christianity shifted east to St. Andrews, and took on a much more Roman style of worship and lifestyle. Thus ended the influence of Iona as a centre of Christian missionary witness, more or less for the next 350 years.