Celtic language decline in England

Prior to the 5th century AD, most people in Great Britain spoke a Brittonic language, but the number of these speakers declined sharply throughout the Anglo-Saxon period (between the 5th and 11th centuries), when Brittonic languages were displaced by Old English.

Debate continues over whether this change was due to mass migration or to a small-scale military takeover by people who spoke the West Germanic dialects that became Old English. The situation in post-Roman Britain was certainly strikingly different from, for example, post-Roman Gaul, Iberia or North Africa, where invaders speaking other languages 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 emergence 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.