An appraisal is made of the part played by lichens in the deterioration of stonework. Stone- and artwork in exposed and partially enclosed environments of Central Italy were examined in detail to identify those substrata most vulnerable to lichen attack. Assessment of relationships between particular species and the physical and chemical nature of their substrata was carried out in order to determine the relative importance of lichens in biodeterioration processes obtaining in specific circumstances, and to establish those species responsible for disfigurement and those causing actual destruction. Particular attention is paid to recent environmental changes conducive to increasing detrimental invasion of terracotta, mortar and painted plaster, and reference is made to examples of building materials, statuary and other ornamental carvings, terracotta pots and frescoes, both those in situ at Ostia Antica, Rome and Caprarola (Viterbo) and those relocated in open-air museums, etc.
