A short report on a project which studied the general problem of the weathering of monuments as a result of meteorological and microclimatic factors, atmospheric pollution and biological activity. Field tests were carried out on the cathedrals in Reggio Emilia and Orvieto, the upper and lower basilicas of San Francesco in Assisi, the Parma Baptistery, the Trajan and Aurelian columns in Rome and the horses of San Marco in Venice. Bibliographic references of papers containing project results.