Tracking the migration of Gaelic speakers who crossed the Irish Sea 1,700 years ago and became the Scots
Ireland in the Early Christian period (A.D. 400-1177) was made up of at least 120 chiefdoms, usually described in surviving documents as petty kingdoms, typically having about 700 warriors. One of these petty kingdoms was Dál Riata, which occupied a corner of County Antrim, the island’s northeasternmost part. Around A.D. 400, people from Dál Riata began to settle across the Irish Sea along the Scottish coast in County Argyll. Other Irish migrants were also establishing footholds along the coast farther south, as far as Wales and even Cornwall, but the migrants from Dál Riata were especially noteworthy because they were known to the Romans as “Scotti” and they would eventually give their Gaelic language and their name to all of what is now known as Scotland.
So far as we know, the only people already living in Scotland in A.D. 400 were the Picts, who were first mentioned by Roman writers in A.D. 297. This was in connection with an attack along Hadrian’s Wall, in which the Picts had the help of Irish (Scotti) allies, so connections across the Irish Sea must have already been strong. Roman sources predictably describe their Pictish adversaries as barbarians and mention their use of blue paint, which some historians later interpreted perhaps too literally (Mel Gibson and his friends show up in the film Braveheart slathered with gallons of it). More likely the Picts were heavily tattooed.
The Picts lived mainly in eastern Scotland, north of modern Edinburgh. We know their homeland both from the distributions of Pictish place-names (which typically begin with “Pett” or “Pit”) and the distribution of Pictish symbol stones, which were Pictish equivalents of a medieval coat of arms, each typically bearing the crest of a petty king and that of his father. The rugged west coast was only lightly occupied by Picts or some other Celtic-speaking people. Settlers from Dál Riata apparently established themselves along the west coast without much opposition. By A.D. 490 the population of Scotti was large enough that the head of the little kingdom moved the family seat across from Ireland. The Scotti alternately cooperated with and fought against the Picts for the next few centuries until the two were unified into a single kingdom under Cináed (Kenneth) mac Ailp’n in A.D. 844. After that the Pictish language disappeared, along with the symbol stones and other archaeological traits that had distinguished them from the Scotti.
What the Scottish case and others like it tells us is that migrations by relatively small dominant societies are much more common in human history than many archaeologists have been willing to admit (much less assume), particularly in North America. Typically, the signatures of it have been explained away too easily as evolutionary change in place. There are so many good examples of change associated with the migration of whole societies or dominant subsets of them, that any major change over time that can be observed archaeologically is likely to have involved migration in one of its many forms, however minor. We should be assuming population movement as a first principle rather than denying it.