The Brythonic group includes Breton, Cornish, and Welsh. They are all descendants of British, the Celtic language of the ancient Britons of Caesar's day. The emergence of Welsh, Cornish, and Breton from British as separate languages probably took place during the 5th and 6th cent. A.D. and was a result of the Germanic invasions of Britain. Welsh and Breton have discarded the originally numerous Indo-European cases for the noun and use only one case. Both employ the Roman alphabet for writing. The accent in Welsh and Breton generally falls on the next-to-last syllable, with the exception of a single Breton dialect that has the accent on the last syllable.
Breton today is spoken by more than 500,000 people in Brittany, most of whom are bilingual, speaking also French. It is not surprising that Breton, unlike Welsh, has many loan words from French. Breton is by no means descended from ancient Gaulish, but rather from the Celtic dialects taken by Welsh and Cornish immigrants from the British Isles who were fleeing Germanic invasions and found refuge in Armorica (now French Brittany) in the 5th and 6th cent. A.D. Surviving literary documents in Breton go back only as far as the 15th cent., but the earlier stages of the language are known through glosses and proper names (see Breton literature).
Cornish, the Celtic language of Cornwall, has survived since the late 18th cent. only among bilingual speakers, but it experienced a minor revival in the 20th cent. Estimates of the number of fluent speakers range from a few hundred to a few thousand. Cornish proper names in manuscripts of the 10th cent. A.D. are the oldest recorded traces of the language. A number of Cornish place-names survive, and some Cornish words appear in the English spoken in Cornwall today. The Cornish language is written in the Roman alphabet. It is not noted for an outstanding literature (see Cornish literature).
Welsh (called Cymraeg or Cymric by its speakers) is the language today of over 600,000 people, chiefly in Wales (a western peninsula of Great Britain) but also in the United States and Canada, to which a number of Welsh people have migrated. Most speakers of Welsh in Great Britain also use English. The oldest extant Welsh texts are from the 8th cent. A.D. (see Welsh literature).