On September 1, the British lines, still hanging on to the southern
slopes of the Thiepval Plateau, followed the crest of the ridge north
of the villages of Thiepval, Bazentin-le-Petit and Longueval, in front
of the outskirts of Delville Wood, were then deflected south-east and
joined with the French lines in the ravine of the Combles railway. The
French lines surrounded Maurepas, then followed the road from Maurepas
to Cléry. Thiepval and Combles seemed impregnable.
Instead of making a frontal attack against these positions, the Allies
first turned and then surrounded them by a succession of thrusts.
In addition to their successive lines of defence-works, which included
a number of villages, the Germans had transformed the little town of
Combles, lying entirely hidden from view at the bottom of an immense
depression--into a redoubtable fortress. A large garrison was safely
sheltered in vast quarries connected by tunnels with the concrete
defence-works.