At the beginning of the fourteenth century, anarchy in Italy led to the capital of the Christian world being moved from Rome for the first and only time in history. It was a critical moment, and it resulted in seven successive popes remaining in exile for the next seventy years. The city chosen to replace Rome was Avignon. And depending on where you stood at the time they were seventy years of heaven, or of hell opinions invariably ran to extremes, as did the behaviour of the popes themselves. It was during this period of exile that the city witnessed some of the most turbulent events in...