According to the Byzantine scholar Andronicus Callistus, the fall of Constantinople to the Ottoman Turks on 29 May 1453 was a cataclysm of such magnitude that it was mourned not only by the Greeks, but by people of every nation. This may sound like the type of rhetorical flourish with which Byzantine authors were fond of adorning their works, yet recent scholarship has tended, if anything, to corroborate Callistus' assertion. Over the past few years, historians of the crusades have been largely successful in showing that the fifteenth century, far from witnessing the decline of the crusading ideal, was a period when it remained as potent as ever, even in a country as far removed from the main theatres of action as England. Consequently, the fall of such an important Christian city was greeted with shock and anger throughout western Europe, and for the rest of the century the burning question for crusading strategists was how the disaster could be reversed.

It is of course true that no large-scale expedition was ever launched against the Turks after 1453, the efforts of successive popes ultimately failing to organise a united Christian response. Yet this does not detract from the overwhelming evidence that all sections of western society took the threat posed to Christendom very seriously, and continued to believe that to take up arms against the infidel was one of the highest acts of piety.