sentences:  An emergency repair to the base of the northwest tower, carried out in 1944 using poor-quality brick taken from a nearby ruined building, remained visible as a reminder of the war until 2005, when it was decided to restore the section to its original appearance.Repair and maintenance work is constantly being carried out in one or another section of the building, which is rarely completely free of scaffolding, as wind, rain, and pollution slowly eat away at the stones.The "Dombauhütte", established to build the cathedral and keep it in repair, is said to employ the best stonemasons in the Rhineland.