 He was successively Professor of Medieval History and Dean of the Faculty of Arts at University of St Andrews, Lecturer in Medieval History at the University of Edinburgh, Professor of Medieval History at the University of Nottingham (1966-1973) and again Professor of Medieval History at St Andrews (1973-1991).He was made Corresponding Fellow of the Monumenta Germaniae Historica in 1983.A collection of essays under the title "Early Medieval Rome and the Christian West