Southwestern Brythonic is one of two dialects into which the Brythonic language split following the Battle of Deorham in 577 CE; the other being Western Brythonic , which later evolved into Welsh and Cumbric. It is believed to be the common ancestor of Cornish and Breton. It has recently been the subject of a minor revival in Devon following the self-publication of a booklet entitled A Handbook of West Country Brythonic: The Forgotten Celtic Tongue of South West England C.700 A.D. (Old Devonian) by Joseph Biddulph, though the merits of Biddulph's attempted reconstruction of the language are strongly disputed by Celtic linguists.