The Mares of Diomedes , also called the Mares of Thrace, were four man-eating horses in Greek mythology. Magnificent, wild, and uncontrollable, they belonged to the giant Diomedes (not to be confused with Diomedes, son of Tydeus), king of Thrace, son of Ares and Cyrene who lived on the shores of the Black Sea. Bucephalus, Alexander the Great's horse, was said to be descended from these mares.