A CENTAUR is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. The most common theory holds that the idea of centaurs came from the first reaction of a non-riding culture, as in the Minoan Aegean world, to nomads who were mounted on horses. The theory suggests that such riders would appear as half-man, half-animal. Bernal Díaz del Castillo reported that the Aztecs also had this misapprehension about Spanish cavalrymen.