glens in the Highlands. To the Roman historians Tacitus and Cassius Dio, the Scottish Highlands and the area north of the River Forth was called Caledonia. According to Cassius Dio, the inhabitants of Caledonia were the Caledonians and the Maeatae. Other ancient authors used the adjective "Caledonian" to pertain to anywhere in northern or inland Britain, often mentioning the region's people and animals, its cold climate, its pearls, and a noteworthy region of wooden hills () which the 2nd-century AD Roman philosopher Ptolemy, in his Geography, described as being south-west of the Beauly Firth. The name Caledonia is echoed in the place names of Dunkeld, Rohallion, and Schiehallion. The Great Conspiracy against Roman rule in Britain in the later 4th century, in which the Scoti participated, was defeated by the comes Theodosius. The formation of a new province, called Valentia after the reigning emperor Valens (), which may have been in Scotland, resulted. Roman military government was withdrawn from the island altogether by the early 5th century, resulting in the Anglo-Saxon settlement of Britain and the immigration of the Saxons to southern Scotland and the rest of eastern Great Britain. Middle Ages Beginning in the sixth century, the area that is now Scotland was divided into three areas: Pictland, a patchwork of small lordships in central Scotland; the Anglo-Saxon Kingdom of Northumbria, which had conquered southeastern Scotland; and Dál Riata, founded by settlers from Ireland, bringing Gaelic language and culture with them. These societies were based on the family unit and had sharp divisions in wealth, although the vast majority were poor and worked full-time in subsistence agriculture. The Picts kept slaves (mostly captured in war) through the ninth century. Gaelic influence over Pictland and Northumbria was facilitated by the large number of Gaelic-speaking clerics working as missionaries. Operating in the sixth century on the island of Iona, Saint Columba was one of the earliest and best-known missionaries. The Vikings began to raid Scotland in the eighth century. Although the raiders sought slaves and luxury items, their main motivation was to acquire land. The oldest Norse settlements were in northwest Scotland, but they eventually conquered many areas along the coast. Old Norse entirely displaced Gaelic in the Northern Isles. In the ninth century, the Norse threat allowed a Gael named Cináed mac Ailpín (Kenneth I) to seize power over Pictland, establishing a royal dynasty to which the modern monarchs trace