Brythonic

The Brythonic languages form the P-Celtic branch of the Insular Celtic family. They descend from Common Brittonic, spoken across most of Roman Britain; after the Roman withdrawal the Anglo-Saxon advance drove the Britons westward and northward, and the Battle of Dyrham in 577 cut the south-western Britons off from the Welsh. The old common language split into Welsh, Cornish and Breton, the last taking shape in Brittany from the fifth and sixth centuries, together with Cumbric and perhaps Pictish.

Cornish ceased to be a living community language by the late eighteenth century. Welsh held its ground, though the Laws in Wales Acts of 1536 and 1542 made English the language of law and administration; William Morgan's Welsh Bible of 1588 and dictionaries in 1632 and from 1770 to 1794 fixed a literary standard.