The Cornish language separated from the southwestern dialect of Common Brittonic at some point between 600 and 1000 AD. The phonological similarity of the Cornish, Welsh, and Breton languages during this period is reflected in their writing systems, and in some cases it is not possible to distinguish these languages orthographically. However, by the time it had ceased to be spoken as a community language around 1800 the Cornish language had undergone significant phonological changes, resulting in a number of unique features which distinguish it from the other neo-Brittonic languages.