The perfection of ancient building technique assured the strong resistance of the monuments to natural forces for a long time. Yet, in many cases, human activity upset the balance of the ancient construction, leaving the monument more susceptible to damage by the forces of nature. It is notable, however, that most of the damage that we are obliged to confront today does not originate in the action of the elements but in the interference of man. Moreover, the damage caused by rescue or restoration interventions of the recent past is extensive. The failure of these interventions lies mainly in the use of ordinary iron for joining fragments of architectural members or for increasing the durability of others.
Most of the damage suffered by the monuments and now being confronted in the framework of the contemporary interventions falls into the following categories:
A. Mechanical: this includes damage wrought by earthquakes, explosions, bombardments, fires, freezing, and by the swelling of rusting iron reinforcements used in the interventions of the recent past.
B. Chemical: this comprises forms of erosion suffered by the marble mainly as a result of acid rain. A serious problem connected with atmospheric pollution concerns the various accretions and deposits in the form of powder, carbon (black soot) and metal rust.
C. Biological: these are forms of corrosion caused by lichens, moulds, bird-droppings, plant roots and their discharges.