German soldiers of the Landwehr Infantry Regiment 99 sheltered in a cave dug into the sides of Hartmannswillerkopf (Vieil Armand in French) near Mulhouse in spring 1916. Numerous underground facilities were dug into the rock by the Germans to strengthen this strategic position (France, World War I). Photograph: Hans Hildenbrand - collection Noëlle and Jean-Noël Deletang.