For centuries, people have used animals to help with work. They used large animals for hard physical work. The horse is irreplaceable on that scale. In addition to serving as the primary and only means of transportation for centuries, the horse was also used for other purposes such as plowing the land, transporting heavy loads, and the like. In addition to horses, oxen and donkeys were used to cultivate the land. Even today, in "third world" countries that are not sufficiently industrially developed, large animals are used as helpers in heavy physical work, especially in rural areas.
