Perhaps the most obvious of these changes was the much
greater military
efficacy of northwestern European society from the eleventh century
onward, as feeble defense gave way to formidable aggression. This was
most evident on the frontiers of Christendom. Knights from the
northwest played roles of varying prominence in the reconquest of Spain
and Sicily from the Muslims, the establishment of Crusader states in
the eastern Mediterranean, and the conquest of pagan territory in the
northeast. But the military edge of the old northern cradle of the
Frankish state was also manifested within the boundaries of the
Christian world by conquests in England, Ireland, and the south of
France. The military basis of these developments was a particular use
of an invention of the early Middle Ages that reached Europe from the
east-the stirrup. The Franks and those who fought like them used it to
perfect a style of warfare in which the ultimate weapon was the
disciplined charge of heavily armored cavalry. As a Byzantine princess
remarked of the Franks, "a mounted knight is irresistible; he would
bore his way through the walls of Babylon." An army of this kind went
well with the domination of peasant society by a warrior aristocracy.