According to the opinion of the author, buildings, stone sculptures, and medieval stained-glass windows are threatened by acid rain. Not earlier than in 1973 it could be proved that there is a connection between the effects of emissions of air pollutants and the decay of stone. Though chemical weathering is admitted since 1859, the present period is claimed to be of a peculiar aggressivity. Acid rain is held responsible for the increased decay of stone, due to the tremendous increase in air pollutants during the last years.