The book concerns a major medieval monument in an urban environment. It discusses previously overlooked material which calls into question the conventional reconstruction of the building history. Correspondingly, it offers a reappraisal of the building's transmutations over several periods, from the Romano-Christian to the Romanesque. It examines each building phase from several viewpoints: the historical circumstances of construction, the expectations of patrons, the urban preconditions of the time, the structural issues faced by the builders, architectural design, usage, fixtures, decorations, and the significance of all for contemporary and subsequent generations.