Page "Battle of Verdun" Paragraph 7

The forts situated to the north and east of Verdun ( e. g. Fort Douaumont, Fort Vaux, Moulainville ) had been thoroughly hardened during the early 1900s with very thick steel-reinforced concrete tops resting on a sand cushion.

Those hardened forts had also been equipped with regular field guns installed in reinforced concrete bunkers (" Casemates de Bourges ") looking sideways, thus providing flanking fire across the intervals between the forts.

However, several large forts built during the 1880s on the same defensive ring, but to the west and south of Verdun ( e. g. La Chaume, Regret, Belrupt-en-Verdunois ), had never been improved.