Peter Kidson, who has died aged 93, was an outstanding historian of medieval architecture whose work and teaching inspired successive generations of scholars.
His special interest, the subject of his PhD thesis, Systems of Measurement and Proportion in Early Medieval Architecture (1956), lay in the transmission of ancient traditions of designing and setting out buildings that passed unbroken into the usages of medieval masons.
Most of his students could not fully understand the regular solids – the basis of the proportional ratios or their numerical equivalents – in the buildings of that period, but all could appreciate the effect they had on planning and structure, which made studying medieval architecture with Peter, always viewed within the intellectual context of its time, especially rewarding.
Born in York, Peter was the son of John Kidson, a merchant navy radio operator, and his wife, Olive (nee Slater). After the family moved to Kent, Peter went to Dartford grammar school, then won a scholarship to Selwyn College, Cambridge, in 1946, where he studied history and moral sciences.
From there he went to the Courtauld Institute of Art for postgraduate study, also attending lectures by Jean Bony at the French Institute. Bony’s European outlook and interest in structure was unusual in 1950s Britain and inspired Peter’s great love of French Gothic architecture.
In 1959 he was appointed the Courtauld’s Conway librarian, teaching at the Courtauld and as a visiting lecturer at Cambridge and the University of East Anglia. He was appointed lecturer at the Courtauld in 1967, and stayed there until retiring as professor in 1990.
Both in the seminar room and on visits to buildings Peter demanded rigorous observation and analysis. He treated his doctoral students, of which I was one of the first, with the same wry detachment with which he observed the modern world, never imposing his own opinion, but allowing his students to pursue their studies as they wished, provided they could defend their position. If they could, all well and good, especially if the encounter was accompanied by the exchange of amusing gossip.
He was one of the most stylish writers on art history of his generation and his published work is both scholarly and accessible: Sculpture at Chartres (1958), the medieval section of A History of English Architecture (1962) and The Medieval World (1967) are all characterised by an invigorating clarity that keeps the reader turning the pages. His article on Architectural Proportion in the Grove Dictionary of Art (1995), a summary of the ideas in his unpublished thesis, demonstrates the originality of his thinking on the subject.
Peter is survived by his second wife, the architectural historian Sarah Pearson, whom he married in 1983, his son, Alex, from his former marriage, to Pamela Bell, which ended in divorce, and his grandson, Patrick.