From 'A History of the British Nation' by AD Innes, 1912
Picts and Scots
Fifty years before the Roman evacuation new names appear for the races outside the Roman sphere which were beginning to surge against the Roman barriers in Britain as elsewhere. We hear of the Picts and Scots and the Attacotti, who, acting sometimes in conjunction with the Saxon rovers, began to descend upon the coasts of Britain or dash themselves against the Roman wall and even to burst through. "Picts" and "Attacotti” must be taken as merely new names for the northern peoples hitherto classed together as Caledonians. The Scots, on the other hand, were certainly Gaelic tribes from the north of Ireland, who were presently to establish themselves in what is now Argyle, and from the kingdom there set up were to extend their name over the whole northern region. But we have now reached the point when the character of these peoples outside Roman Britain calls for further consideration.
Who were the Picts?
It has been laid down as a general proposition that the Scottish highlands were occupied by Goidelic Celts, Gaels; and it may further be laid down that Galloway, roughly speaking the triangle between the Firths of Clyde and Solway, was also mainly occupied by Gaels, not by Brythons, whatever may have been the case with the eastern lowlands. Presently we shall find Argyle and the Isles in possession of colonies of Scots from Ireland. The name of the Attacotti will disappear; but who were the Picts who apparently held sway over the greater part of the country? The ethnological experts are very much at variance on the subject. On the one side are those who urged that they were simply Goidelic Celts; on the other side are those who do not recognise them as Aryans at all; while a third, but now wholly discredited, theory attributed to them a Teutonic origin. A detailed examination of the question is here impracticable; but perhaps the strongest argument in favour of the non-Aryan theory is the indubitable prevalence among them of the tracing of hereditary descent through the mother instead of through the father, a practice which is affirmed to be non-Aryan.
At the same time, although among the Aryan races in historic times descent was always traced through the father, there are indications that this had not always been the case; and it is quite conceivable that in one branch of the great Aryan family the other system may have proved victorious. The very inconclusive evidence seems to point to the language of the Picts being Gaelic, mainly because Gaelic was certainly the language which survived, and there is no definite indication that another tongue was spoken. On the whole the presumption is distinctly in favour of the Gaelic theory, in spite of the difference between the Pictish law of succession and that which prevailed among the Aryan peoples at large, including the rest of the Celts, Gaelic as well as Brythonic.
The Celtic north
The position then in the British Islands at the time of the Roman evacuation may be thus summarised, Ireland had not been touched by the Romans, and was wholly Celtic, apart from the survival of an Iberian element. What we now call Scotland was wholly Celtic, unless it is after all true that the Picts were not Aryans at all. Neither Ireland nor Scotland was as yet Christianised, and Scotland, too, had been untouched by Roman ideas and Roman culture, and had never really been brought under Roman domination.
The Romanised south
On the other hand, the greater part of the larger island, practically corresponding to what we now call England and Wales, had been under Roman dominion for more than three hundred years; there was probably an actual Roman element in the upper classes; there was a considerable infusion of Roman culture in the towns which had grown up at the Roman centres; Celtic customs had been in some degree modified contact with Roman law, but still the Britons were the least Romanised of all the Western peoples who had come under the Roman sway, as may be most definitely seen in the fact that the Roman language disappeared, whereas in Spain and in Gaul, as well as in Italy, Latin had been so thoroughly adopted that it prevailed even over the Teutonic conquerors.