Those peoples which early acquired the resources in the way of strength and fleetness which the horse put at their disposition, became inevitably the conquerors of the folk who were denied these advantages. If we consider the conditions which have led to the domination of the world by the Aryan and Semitic people, and the races which they have affiliated with them, we readily discern the fact that they have, to a great extent, won by horse-power rather than by their own physical strength. Thus equipped by their able servants, they have pressed outward from their ancient realms and have in a way overridden the tribes which were unmounted. So imposing is the effect of the horsed man on all peoples who are without previous knowledge of the united creatures, that it always carries fear to their hearts. To such folk the combination appears as a single terrible being. The ease with which the Spaniards conquered Mexico and Peru can, to a great extent, be attributed to the awe carried into the ranks of the savage footmen by their mail-clad horses. The Greeks, who were wont to represent the forces of nature and the accomplishments of man by skilfully constructed myths, have left a record showing their appreciation of the strength derived from the union of horse and man, in their fable of the Centaur, which possibly grew up in a time before their people had won the use of the animal, and when they only knew the creature by chance encounters with enemies who were mounted upon them. Although the naturalist of to-day perceives the impossibility of there ever having been on this earth a form uniting the trunk and fore-limbs of a quadruped to the upper part of a man's body, such scientific conceptions are a part of our modern, recently acquired store of knowledge. To the Greeks of the myth-making age the creature, half man, half horse, added but one more wonder to the vast store the world already contained. The currency of this fable shows us very clearly how great was the impression which the horse made upon primitive peoples.