“The Caspian is thought to be one of the oldest horse or pony breeds in the world today, dating back from the now-extinct miniature horses of Mesopotamia, who lived in the region from 3,000 BCE until the 7th century. The ponies now inhabit an area between the Caspian Sea and the Elburz Mountains, although new groups of horses potentially related to the Caspian have been identified in a much wider range.”
http://en.wikipedia.org/wiki/Caspian_Pony
The idea is that the horse was demonstrated to be so valuable so quickly that ALL of them were caught and put to the bridle, with their breeding controlled.