In 1294, Peter of Morrone—San Celestino, little St. Celestine, as popular devotion calls him—was elected pope of the Holy Roman Catholic and Apostolic Church. The Spirit moves where it will; perhaps a shy, ascetic monk was necessary at that moment, to remind the church of its truest calling. The college of cardinals thought so, at least, desperate after two years of failing to choose a successor to Nicholas IV.

Still, no one should have been surprised that a man who had previously lived as a hermit in a cave in Abruzzi would prove one of the least competent administrators the world has ever seen. He never actually made it to Rome, ruling—if the word is allowed a certain looseness—from Naples and attempting such governance practices as disappearing for the whole...