German field fortifications continued to be defended by machine-gun fire, artillery-fire and swift local counter-attacks, extra heavy artillery brought from Verdun, was used to extend bombardments beyond the Allied front line, to artillery positions and supply routes. New German defensive works were harder to spot, during the fewer periods of good flying weather, often not being revealed until attacking infantry were engaged from them. The Germans also gained an advantage, from being forced back, as the area most devastated by artillery-fire grew wider and was on the Allied side, which created chronic problems in transporting supplies to the front line, periodically made worse by downpours, which turned roads and tracks into glissades of mud. It was far easier for supplies to be brought up to the German front line, as it was pushed back along supply lines that had been established for two years.