Grado Giovanni Merlo: is professor emeritus of the history of Christianity at the University of Milan, founder of the journal “Quaderni di storia religiosa” and member of the editorial board of the “Italian historical journal”. He dedicated his research to Christianity in the late Middle Ages, with regard to the origins and evolution of the Franciscan movement, to the relationship between Orthodoxy and heresy and to the role of the papacy and ecclesiastical institutions in the history of the Latin West. Among his recent publications: Valdo. L’eretico di Lione (Torino 2010); Streghe (Bologna 2011); Giovanni Miccoli (Brescia 2011); Eretici ed eresie medievali (Bologna 2011); Il cristianesimo medievale in Occidente (Roma-Bari 2012); Frate Francesco (Bologna 2017).