L 11.50 naval & Military Press ISBN 1-84747-15 1
This is about the permanent French fortificaions of WW1, excellent! It does not pretend to be about the battle though it's discussed, rather the reasons for the location of forts, their design, some history of older works how they were modernized because of developments in artillery and powder etc. Excellent discussion of French planning after Franco Prussian war, the first 15 plans were nearly strictly defensive but the process ended with Joffre's famous Plan XVII. Earlier plans relied heavily on the forts and other structures but 17 did not. After war began French took note of the destruction of Belgian forts and that + a great need for artillery caused removal of guns and a decrease in # & quality of garrisons.'
Of course it was later learned the the interior of these forts held up well and served as great shelters for troops of both sides.
Of course these forts are still there and this along with Christina Holstein's excellent Walking verdun will be quite helpful to visitors.