Nor were the Crusades “thoughtless explosions of barbarism,” as Riley-Smith accurately characterizes their reputation today. They had a sophisticated underlying rationale, elaborated theologically by Christian nations threatened by Muslim invaders who had managed to reach into the heart of Europe — from central France in the eighth century to Vienna in the sixteenth and seventeenth centuries. They were a response to the desecration of Christian shrines in the Holy Land, the destruction of churches there and the general persecution of Christians in the Near East. A Crusade had to fulfill strict criteria for the Church to consider it legitimate and just. It had to be waged for purposes of repelling violence or injury, with the goal of imposing justice on wrongdoers. A Crusade was not to be a war of conversion but rather a rightful attempt to recover unjustly seized Christian territory. And only a recognized church authority like the pope could call for one.