This ambitious book is about a way of building that for centuries dominated the making of monumental architecture – yet now not only is it lost as practice, but knowledge of its very existence is consigned to oblivion. In pre-modern Europe, the architect built not just with imagination, brick and mortar, but with time, using vast quantities of duration to erect monumental buildings that otherwise would have been impossible. Not mere medieval muddling-through, this entailed a sophisticated set of norms and practices. Virtually all the great cathedrals of France and the rest of Europe were built under this regime, here given the name ‘Building-in-Time’. In particular, the major works of pre-modern Italy, from the Pisa cathedral group to the cathedrals of Milan,Venice and Siena, and from the monuments of fourteenth-century Florence to the new St Peter’s – the apotheosis of the practice – are thus cast in an entirely new light.