This study carried out in the protected area of Bordeaux was undertaken with the help of a research contract partly financed by the Ministry for the Quality of Life. Its aim was to establish the relationship between the state of the stones and their immediate or remote environment. Investigation of the various causes of deterioration led to a study of the geology and the hydrogeology of the sub-soils in the old town and to a study of atmospheric pollution. A very clear relationship was established between atmospheric phenomena and deterioration in the upper parts of buildings.