Celtic language decline in England

Prior to the 5th century AD, most people in Great Britain spoke the Brythonic languages, but these numbers declined sharply throughout the Anglo-Saxon period (between the fifth and eleventh centuries), when Brythonic languages were displaced by the West Germanic dialects that are now known collectively as Old English.

Debate continues over whether mass migration or a small scale military takeover occurred during this period, not least because the situation was strikingly different from, for example, post-Roman Gaul, Iberia or North Africa, where Germanic-speaking invaders gradually switched to local languages. This linguistic decline is therefore crucial to understanding the cultural changes in post-Roman Britain, the Anglo-Saxon settlement of Britain and the rise of an English language.

The notable exceptions were the Cornish language persisting into the 18th century, and a form of Welsh remaining in common usage in the English counties along the Welsh border into the late 19th century.