British soldier passes the iron frameworks of a German pillbox at Broodseinde. The German practice of defending frontline trenches regardless of casualties was abolished, in favor of a mobile defense of the fortified areas being built over the autumn and winter of 1916-17. Trenches became mainly intended for accommodation, supply dumps and to act as decoys rather than be firing lines. Deep dugouts in the front line were replaced by many more smaller shallow Mannschafts-Eisen-Beton-Unterstande (pillboxes) with most built towards the rear of the defensive areas. Pillboxes are concrete dug in guard posts, normally equipped with loopholes through which to fire weapons. The Battle of Broodseinde was fought on October 4, 1917 near Ypres in Flanders by the British Second and Fifth armies and the German Fourth Army. The battle was the most successful Allied attack of the Battle of Passchendaele.