The Welsh language emerged from the increasing dialect differentiation of the ancestral Brythonic language (also known as British or Brittonic) in the wake of the withdrawal of the Roman administration from Britain and the subsequent migration of Germanic speakers to Britain from the fi fth century. Conventionally, Welsh is treated as a separate language from the mid-sixth century. By this time, Brythonic speakers, who once occupied the whole of Britain apart from the north of Scotland, had been driven out of most of what is now England. Some Brythonic speakers had migrated to Brittany from the late fi fth century. Others had been pushed westwards and northwards into Wales, western and south-western England, Cumbria and other parts of northern England and southern Scotland. With the defeat of the Romano-British forces at Dyrham in 577, the Britons in Wales were cut off by land from those in the west and south-west of England. Linguistically more important, fi nal unstressed syllables were lost (apocope) in all varieties of Brythonic at about this time, a change intimately connected to the loss of morphological case. These changes are traditionally seen as having had such a drastic effect on the structure of the language as to mark a watershed in the development of Brythonic. From this period on, linguists refer to the Brythonic varieties spoken in Wales as Welsh; those in the west and south-west of England as Cornish; and those in Brittany as Breton. A fourth Brythonic language, Cumbric, emerged in the north of England, but died out, without leaving written records, in perhaps the eleventh century.