Adamnan, in his Life of St. Columba, mentions that the saint being on a visit to Bruide Mac Meilcon, king of the Northern Picts, at his stronghold on the river Ness, requested the king to recommend to the _reguli_ of the Orkneys (one of whom was then present, and whose hostages were then in the king’s hands) that Cormac and the clerics who had accompanied him on a missionary voyage to the Orkneys should receive no harm; and it is added that this was the means of saving them from a violent death. But if the authority and influence of the king of the Northern Picts extended to these islands in the reign of Bruide, it does not seem to have been effectual in protecting them from foreign invasion. Bruide Mac Meilcon died in 584, and some time before his death the new and rising power of the Dalriadic kings had made itself felt as far as the Orkneys. In the Annals of Ulster there is a notice under the year 580 of an expedition against the Orkneys by Aedan, son of Gabran, seventh king of the Dalriad Scots, who, coming over from Ireland (then called Scotia) about the year 503, had established themselves in Argyle and the Western Highlands, and founded the kingdom of Dalriada. From the date of Aedan’s expedition in 580 we have no mention of the islands in the native chronicles for a whole century, and the next entry, which occurs under the year 682, gives colour to the supposition that they may have been under Dalriadic rule in the interval. The record in 682 is simply, that the Orkneys were wasted by Bruide Mac Bile, the king of the Northern Picts, and apparently brought once more under the rule of the Northern Pictish kings.
It is probable that both the island groups of Orkney and Shetland were visited at a very early period by wandering clerics of the Irish Church, whose missionary efforts contributed so much to the diffusion of Christianity in Scotland. But we have no record of an earlier visitation than that of the companions of St. Columba, although there are indications that between that time and the colonisation of the islands by the heathen Northmen, these Irish clerics were no strangers in any of the island groups.
The Irish monk Dicuil, who wrote his treatise “De Mensura Orbis Terrarum” in or about the year 825, states that “thirty years before that time some clerics had told him that they had lived in an island which they supposed to be Thule, where at the summer solstice the sun only hid himself behind a little hill for a short time during the night, which was quite light; and that a day’s sail towards the north would bring them from thence into the frozen sea.” This island is obviously Iceland. He then states that there are many other islands in the northern British sea, which lie at the distance of two days and two nights from the northern islands of Britain, in a straight course, and with a fair wind and a full sail. “One of these,” he says, “a certain honest monk told me he had visited one summer after sailing a day, a night, and another day, in a two-benched boat.” These appear to be the Shetland Islands. Dicuil further states that “there are also some other small islands, almost all divided from each other by narrow sounds, inhabited for about a century by hermits proceeding from our Scotia;[4] but as they had been deserted since the beginning of the world, so are they now abandoned by these anchorites on account of the Northern robbers; but they are full of countless sheep, and swarm with sea-fowl of various kinds. We have not seen these islands mentioned in the works of any author.” Here the reference to the “small isles separated by narrow sounds” is distinctive of the Faroes, of which the long narrow sounds are the peculiar physical feature; while the statement that they are full of countless sheep, taken in connection with the fact that the Northmen named them “Sheep-isles” (Fær-eyiar), establishes the identity of the group which Dicuil describes. The Faroes were colonised by “the Northern robbers,” led by Grim Kamban, in 825, the very year in which Dicuil was writing.