SOURCE: “The Further Development of the Popular Idea of Crusade” in The Origin of the Idea of Crusade, translated by Marshall W. Baldwin and Walter Goffart, Princeton University Press, 1977, pp. 269–305.

In the following essay, Erdmann analyzes the various elements—including religious and literary developments—that enabled the “general idea of crusade and war upon the heathen” to take the specific form of the Crusade to the Holy Land.

Gregory VII's idea of a hierarchical crusade brought general discord rather than united action; alongside it the popular idea of crusade led a life of its own.¹

The socioeconomic conditions for the crusading movement were largely present in the second half of the eleventh century, as best illustrated by the fact that a free mercenary soldiery acquired increasing prominence at this time.² While mercenaries had been regularly used at Byzantium since late Antiquity, the West had rarely seen knights, or...