The first written reference to Scotland was in 320 BC by Greek sailor Pytheas, who called the northern tip of Britain “Orcas”, the source of the name of the Orkney islands. During the first millennium BC, the society changed dramatically to a chiefdom model, as consolidation of settlement led to the concentration of wealth and underground stores of surplus food.
The Roman conquest of Britain was never completed, and most of modern Scotland was not brought under Roman political control. The first Roman incursion into Scotland occurred in 79 AD, when Agricola invaded Scotland; he defeated a Caledonian army at the Battle of Mons Graupius in 83 AD. After the Roman victory, Roman forts were briefly set along the Gask Ridge close to the Highland line, but by three years after the battle, the Roman armies had withdrawn to the Southern Uplands. Remains of Roman forts established in the 1st century have been found as far north as the Moray Firth. By the reign of the Roman emperorTrajan (r. 98–117), Roman control had lapsed to Britain south of a line between the River Tyne and the Solway Firth. Along this line Trajan’s successor Hadrian (r. 117–138) erected Hadrian’s Wall in northern England and the Limes Britannicus became the northern border of the Roman Empire. The Roman influence on the southern part of the country was considerable, and they introduced Christianity to Scotland.
The Antonine Wall was built from 142 at the order of Hadrian’s successor Antoninus Pius (r. 138–161), defending the Roman part of Scotland from the unadministered part of the island, north of a line between the Firth of Clyde and the Firth of Forth. The successful Roman invasion of Caledonia 208–210 was undertaken by emperors of the imperial Severan dynasty in response to the breaking of treaty by the Caledonians in 197, but permanent conquest of the whole of Great Britain was forestalled by the death of the senior emperor Septimius Severus (r. 193–211) while on campaign at Eboracum (York), and the Caledonians were again in revolt in 210–211. Forts erected by the Roman army of the Severan campaign were placed near those established by Agricola and were clustered at the mouths of the 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 (Latin: saltus) 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 (r. 364–378), 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.