A must. Two atlas the same author, are complementary: one, and "The Atlas of fortified towns and villages in France [] (same publisher) constituting a very good 'bible'. The presentation of maps of regional 'or' departmental '- with the positioning of the sites - provides a very valuable approach. One downside (minor, easy to overcome), it lacks - on each card, the reference adjacent cards, forcing either flipping or to supplement the information or even add a general assembly board (returning each entity its geographical neighbors). Useful - for example - the limit of the department, not to stop at a 'border' artificial (especially for the time being).
Both books can be usefully complemented by the "Mesqui" ["Castles and pregnant] if you want to accentuate the architectural approach and better understand the evolution and the" Viollet-le-Duc "[" Encyclopedia medieval "] (Commentary almost identical to that of "cities", the two atlases with the same qualities and minor defects.)