Five hundred years ago an obscure Augustinian monk in the small university town of Wittenberg carried out an act of protest that is widely recognised as a watershed in western European history. Though scholars now debate what exactly took place on 31 October 1517, the nailing of Martin Luther’s 95 theses against indulgences and the papacy’s power to pardon sin to the door of the castle church has acquired a pivotal place in the historical imagination. It has become a shorthand for the beginning of the movement that we call the Reformation.