Siena cathedral_Earthquakes and the re-evaluation of the construction concept of the cathedral

The numerous, and at times violent, earthquakes resulted in the use in Siena cathedral of all the construction devices that medieval builders had chosen not to use: buttresses, chains and flying buttresses. It was a gradual and discontinuous process and not the result of a preventive analysis of the construction aspects of the dome and its vulnerabilities. Rather, decisions were based on conditions of necessity with respect to the serious damage suffered by different parts of the building in several episodes between the 17th and 18th centuries. These unrelated interventions as a whole, also carried out at considerable time intervals, became widespread and affected the whole building.