During the spring of 1917 the German forces on the Western Front vountarily retired from the positions in the Somme at Serre, which they had defended with such stubborness in 1916, to the famous Hindenburg line, an intricate system of heavily fortified trenches between the Vimy Ridge on the north and the Chemin des James ridge in the south. In the back ground of the photograph there is a sign saying "Old Hun line".