Peter D. Clarke is Professor of Medieval History at the University of Southampton and President of the International Society of Medieval Canon Law. His publications include The Interdict in the Thirteenth Century: A Question of Collective Guilt (2007) and Supplications from England and Wales in the Registers of the Apostolic Penitentiary, 1410-1503 in three volumes (co-edited with Patrick N R Zutshi, 2013-15).