My principal research interest is the canon law of the medieval Western Church, an international legal system that touched the lives of Christians and non-Christians in the Medieval West. My doctoral work (later developed into a monograph) focussed on the interdict, a sanction of the Western Church that might be imposed on communities, even kingdoms, and had the effect of closing churches and suspending religious rites. Interdicts were usually provoked by a secular ruler’s disobedience to church authorities and often exploited by popes as a political weapon in clashes with such rulers.