The notion that numerical proportional systems contribute to the serene, orderly appearance of the basilica of San Lorenzo has long stood as a virtual axiom of architectural history. In this book, Cohen challenges this and many other longstanding preconceptions about proportional systems in the history of architecture. Using Brunelleschi's basilicas of San Lorenzo and Santo Spirito as case studies the author presents a detailed analysis of his comprehensive measurements of these buildings, which he recorded from scaffolding, meticulous observations of the built fabric, and a variety of documentary sources. This book presents a rigorous new approach to an important but little studied area of architectural history, and is an essential reading for anyone interested in medieval and Renaissance architecture