Topics are treated with the methodological and linguistic rigor specific to each disciplinary sector involved even if, in the interest of making reading and comprehension easier, it was sometimes preferred to present only significant case studies, which are nevertheless representative of groups of wider and more complex problems. Through the reading of this work, the reader can simply fulfil his desire for knowledge and obtain answers to certain curiosities about the past history of the Church. At the same time, useful guidelines in dealing with conservation and restoration interventions at historic-architectural sites of similar complexity can be found. The book is, therefore, addressed to a generic reader, interested in the history and conservation of one of the most representative examples of our heritage, but also, in light of its technical and scientific value, to university students, technicians, restorers, architects, structural engineers, archaeologists and historians.