The author advocates studying cathedrals biographically, tracing how successive alterations reflect changing ritual needs, structural failures, and aesthetic aims rather than pure taste. He surveys causes for enlargement and remodelling—growing saint-veneration, pilgrimages, expanded liturgical space, desires for more light and stained glass—alongside practical triggers such as fire, storm damage, and medieval poor workmanship that provoked collapses and reconstructions. The work combines architectural description, discussion of ground-plans and ichnography, and case studies of individual churches to show how liturgical practice, material limits, and competition shaped form over centuries.