Celtic Britons
The Britons were an ancient Celtic people who lived in Great Britain from the Iron Age through the Roman and Sub-Roman periods. They spoke a language that is now known as Common Brittonic.
The earliest evidence of the existence of the Britons and their language in historical sources dates to the Iron Age. After the Roman conquest of Britain in the 1st century, a Romano-British culture emerged, and Latin and British Vulgar Latin coexisted with Brittonic. During and after the Roman era, the Britons lived throughout Britain south of the Firth of Forth. Their relationship with the Picts, who lived north of the Firth of Forth, has been the subject of much discussion, though most scholars accept that the Pictish language was related to Common Brittonic.
With the beginning of Anglo-Saxon settlement in the 5th century, the culture and language of the Britons fragmented and much of their territory was taken over by the Anglo-Saxons. The extent to which this cultural and linguistic change was accompanied by wholesale changes in the population is still a matter of discussion. During this period some Britons migrated to mainland Europe and established significant settlements in Brittany (now part of France) as well as Britonia in modern Galicia, Spain. By the 11th century, remaining Celtic-speaking populations had split into distinct groups: the Welsh in Wales, the Cornish in Cornwall, the Bretons in Brittany, and the people of the Hen Ogledd ("Old North") in southern Scotland and northern England. Common Brittonic developed into the distinct Brittonic languages: Welsh, Cumbric, Cornish and Breton.