The defeated Iron Age tribes of Britain At the end of the Iron Age (roughly the last 700 years BC), we get our first eye-witness accounts of Britain from Greco-Roman authors, not least Julius Caesar who invaded in 55 and 54 BC. These reveal a mosaic of named peoples (Trinovantes, Silures, Cornovii, Selgovae, etc), but there is little sign such groups had any sense of collective identity any more than the islanders of AD 1000 all considered themselves 'Britons'.
'Calling the British Iron Age 'Celtic' is so misleading that it is best abandoned.'
However, there is one thing that the Romans, modern archaeologists and the Iron Age islanders themselves would all agree on: they were not Celts. This was an invention of the 18th century; the name was not used earlier. The idea came from the discovery around 1700 that the non-English island tongues relate to that of the ancient continental Gauls, who really were called Celts. This ancient continental ethnic label was applied to the wider family of languages. But 'Celtic' was soon extended to describe insular monuments, art, culture and peoples, ancient and modern: island 'Celtic' identity was born, like Britishness, in the 18th century.
However, language does not determine ethnicity (that would make the modern islanders 'Germans', since they mostly speak English, classified as a Germanic tongue). And anyway, no one knows how or when the languages that we choose to call 'Celtic', arrived in the archipelago - they were already long established and had diversified into several tongues, when our evidence begins. Certainly, there is no reason to link the coming of 'Celtic' language with any great 'Celtic invasions' from Europe during the Iron Age, because there is no hard evidence to suggest there were any.
Archaeologists widely agree on two things about the British Iron Age: its many regional cultures grew out of the preceding local Bronze Age, and did not derive from waves of continental 'Celtic' invaders. And secondly, calling the British Iron Age 'Celtic' is so misleading that it is best abandoned. Of course, there are important cultural similarities and connections between Britain, Ireland and continental Europe, reflecting intimate contacts and undoubtedly the movement of some people, but the same could be said for many other periods of history.
The things we have labelled 'Celtic' icons - such as hill-forts and art, weapons and jewellery - were more about aristocratic, political, military and religious connections than common ethnicity. (Compare the later cases of medieval Catholic Christianity or European Renaissance culture, or indeed the Hellenistic Greek Mediterranean and the Roman world - all show similar patterns of cultural sharing and emulation among the powerful, across ethnic boundaries.)
Almost everyone in Britannia was legally and culturally 'Roman' The Roman conquest, which started in AD 43, illustrates the profound cultural and political impact that small numbers of people can have in some circumstances, for the Romans did not colonise the islands of Britain to any significant degree. To a population of around three million, their army, administration and carpet-baggers added only a few per cent.
'The future Scotland remained beyond Roman government, although the nearby presence of the empire had major effects.'
The province's towns and villas were overwhelmingly built by indigenous people - again the wealthy - adopting the new international culture of power. Greco-Roman civilisation displaced the 'Celtic' culture of Iron Age Europe. These islanders actually became Romans, both culturally and legally (the Roman citizenship was more a political status than an ethnic identity). By AD 300, almost everyone in 'Britannia' was Roman, legally and culturally, even though of indigenous descent and still mostly speaking 'Celtic' dialects. Roman rule saw profound cultural change, but emphatically without any mass migration.
However, Rome only ever conquered half the island. The future Scotland remained beyond Roman government, although the nearby presence of the empire had major effects. The kingdom of the Picts appeared during the third century AD, the first of a series of statelets which, during the last years and collapse of Roman power, developed through the merging of the 'tribes' of earlier times.