Located close to the River Somme, Arras was caught up in some of the heaviest fighting on the Western Front during WWI. The town was under constant bombardment throughout the conflict, and the 12,000 Allied troops who were stationed there lived deep underground in a network of caves and tunnels, many of which were lighted by electricity. Arras Cathedral was destroyed by shelling in April 1917 during the run-up to the Nivelle offensives. Once the war was over, Arras Cathedral, the town hall and all the old houses that formed the cobbled market square were rebuilt following the original plans of design as closely as possible, and were finally restored to their former glory by the late 1920s.