The First Crusade was such an important event with such amazing consequences that it is hardly surprising that an enormous amount of ink has been spent on discovering the reasons why enthusiasm for it was so widespread. Much effort has been spent on examining factors which preconditioned the men of the eleventh century to welcome Urban's appeal in 1095–6. Broadly speaking it has been supposed that the wars against Islam in Spain accustomed men to the notion of Holy War, while the growing authority of the Church in the age of reform predisposed them to obey their spiritual directors – early evidence of this was the Peace and Truce of God first proclaimed by the bishops and clergy of France. Papal initiative in supporting the reconquest of Islamic Sicily and ‘corrupt’ England, and the influence of papal ideas about the militia Christi refined and developed by Anselm of Lucca reinforced the point. The Church threw its authority behind pilgrimage, the great manifestation of the popular piety of the age which was intimately allied to devotion to relics of saints and the cult of their sacred places. The most sacred of all places, and therefore the greatest of pilgrimages, was that to Jerusalem. It was the spiritual reward for this journey to Jerusalem which Urban 11 offered for those going on the expedition of 1095. These factors have always been the substance of discussion and were systematically analysed by Erdmann in a book which remains the basis of scholarly discussion to this day.