Linguistic boundary of Brittany

The language boundary in Brittany is the language border between the part of Brittany where Breton (a Celtic language) is spoken and the area in Brittany where Gallo (a Romance language) is spoken. The existence of this linguistic border led to differentiate the Celtic-speaking Lower Brittany (West) from the Romance-speaking Upper Brittany (East).

The farthest eastern extension of the Breton language was in the ninth century, when the linguistic border was located near Nantes and Rennes. Breton declined inexorably in favor of the Gallo gradually moving westward along a Binic-Guérande line. The border can now be traced along a line from Plouha to Rhuys. The linguistic unification of France, completed after World War II, made somewhat obsolete the linguistic aspect of the distinction between Upper and Lower Brittany, although many people still consider it valid in terms of toponymy, culture and identity.

Place-names are one form of evidence for the linguistic boundary during the Early Middle Ages, suggesting that it was much farther to the east than it is now, near Nantes and Rennes. For example, Pleugueneuc, in Ille-et-Vilaine, combines the Breton element plou (parish) with the name 'Guehenoc'.

The distinction of two Brittanys was made at least as early as the 15th century, when the names used were Britannia gallicana (Gallic Brittany) and Britannia britonizans (Brittonic Brittany). At that time, it appears that Lower Brittany had a separate fiscal status. Since then, the boundary between them has changed slowly as a result of the long retreat of the Breton language.

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