Geometry and proportion have always been fundamental to expertise in building; they emerge even in the record of constructing a great temple in the biblical book of Ezekiel. The books on architecture of the Roman author Vitruvius were copied widely and fed directly into the secrets of the medieval lodges, which are now known in part from Villard de Honnecourt’s sketchbook. The disputes at Milan about how to proceed with the cathedral illustrate how the time-honoured rules of proportion persisted, even though their intuitive justifications appeared to be getting lost. Ultimately, Renaissance thinking and the invention of printing opened a new era. This is well represented by St Paul’s Cathedral but also gave rise to the distinction between engineers and architects and the belief that every gentleman with money and a copy of Vitruvius could design his own buildings.