Barr (placename element)
Barr- is a pre-Indo-European linguistic root meaning 'wooded hill', 'natural barrier'. In addition to the common noun bar, it explains many place names as:

 Barr, commune of Alsace, France 
 Bar, commune of Corrèze, Limousin France 
 Bar-sur-Aube and Bar-sur-Seine, communes of Aube, Champagne, France
 Bar-le-Duc, commune of Lorraine, France

but not Le Bar-sur-Loup, a former Albarn > Aubarn. In Alps, the word applies to rocky escarpments:
 la Barre des Écrins is a mountain in French Alps. This root should not be mistaken for the Basque root Bar- / ibar 'valley'. Notes and references

Place name element etymologies
Prefixes