No one has treated the famous Dictatus papae more convincingly than Cowdrey, to whom they mark an early and undeveloped stage in the Pope's thinking ... Gregory's personality was so towering, many of his acts so dramatic and the reactions to him so complex that writing his biography is like climbing an academic Everest. Everything Cowdrey has done in a very distinguished career has been leading up to this. It is the culmination of a life's work, and in my view it is a masterpiece.