In the period following the separation of Britain from the continent, there occurred an immigration into Britain from Central Europe of a short-skulled people, who imposed their language and customs upon the neolithic races. While they coalesced with these races, yet to a certain degree they must have remained a ruling or aristocratic caste. In time this short-skulled race spread over the whole of Britain, penetrating to the shores of the Pentland Firth and the islands beyond Cape Orcas. Besides having tools of flint, they used bronze in the manufacture of their weapons. Though the art of smelting iron was unknown to them, they were able to work copper and tin, which they wrought into bronze, and so the period of their civilization is named the Bronze Age. The next immigrants were the Brythons from Gaul, who introduced the use of iron and Celtic art, and who possessed the country when the Romans came. At first called Britons by the Romans, the northern Britons were styled Caledonians by Tacitus, but from the third century were known to the Romans and the southern Britons as the Picts.
The next invasion came from the west. The Scots - a Gaelic race - crossed from Ireland in the Roman period, subdued Argyll and the Western Isles, and encroached gradually upon the Pictish kingdoms. The Gaelic invasion had in the sixth century developed a missionary movement led by Columba, whose followers soon carried the Gaelic language and Gaelic civilization to the remotest corners of the land. Many of the Columban missionaries became identified with northern localities. Dunnet was associated with St Donat, whose chapel is the "fanum Donati" of Buchanan. The patron saint of Wick was St Fergus, who is said to have flourished in the eighth century. It would seem that in the course of the seventh and eighth centuries Gaelic, introduced by the Christian missionaries, rapidly supplanted Pictish (which possesed no written literature), just as in later centuries Gaelic supplanted Norse in the Hebrides.
The Norse began to find their way into Caithness in the ninth century. Norse jarls soon intermarried with the Gaels and settled on the land. Owing to the superior influence of their sea power and the remoteness of Caithness from the seat of Scottish government, the north-eastern part of the county soon fell into the possession of the Norse, who gradually spread over the fertile lowland plains and be came exporters of grain and cattle to barren Norway, The Gaels gradually receded to the less fertile uplands of Latheron, Halkirk, and Reay, while retaining a hold upon parts of Watten and Bower. The partition of the country between Norseman and Gael thus effected in the tenth century remained undisturbed for nearly a thousand years. The place names of the county bear ample testimony to this. Most of the names of hills, streams, lochs, and townships in the upland parishes are of Gaelic origin, a few being Pictish, while the names in the north-eastern or lowland parishes are mainly Norse or English, with a sprinkling of names of Gaelic or Pictish origin.
The population of 32,010 (according to the census of 1911) included 3251 persons who were not natives of the county. Nearly every other county in Scotland contributed a quota of these, but the larger number of them came from the neighbouring counties. The Gaelic-speaking population in 1911 was 1680, mostly in Latheron and Reay, and a smaller number in Halkirk, Thurso, and Watten. Gaelic does not appear to receive any encouragement in the schools and is not largely spoken by the young. The population of Caithness, as of other northern counties, has been steadily declining during the past half century. The Burgh of Wick shows some signs of expansion, but Thurso is practically stationary, while the rural parishes show a steady decline of population at each successive census. The density of the population in Caithness is 46 to the square mile compared with 157 to the square mile for Scotland. Wick contains nearly one-third of the whole population of the county. From rural Caithness, which is almost wholly agricultural, large numbers belonging to the farming community have been emigrating in recent years, chiefly to Canada.
According to the census of 1911 there were employed in the county 494 coopers, 140 millwrights, blacksmiths, and strikers, 73 men fish workers and 196 women fish workers. Carpenters, painters, plumbers, and masons numbered 494, tailors and shoemakers 247, bakers and grocers 268, and general labourers 248. There were 302 women employed as dressmakers. The number of fishermen was 637 while there were 189 fishermen-crofters.