The Mares of Diomedes, also called the Mares of Thrace, were a herd of man-eating horses in Greek mythology. Magnificent, wild, and uncontrollable, they belonged to Diomedes of Thrace, 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

Thrace is a geographical and historical region in Southeast Europe. Bounded by the Balkan Mountains to the north, the Aegean Sea to the south, and the Black Sea to the east, it comprises present-day southeastern Bulgaria, northeastern Greece, and the European part of Turkey, roughly the Roman Province of Thrace. Lands also inhabited by ancient Thracians extended in the north to modern-day Northern Bulgaria and Romania and to the west into Macedonia.