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, 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.
Mythology
As the eighth of his Twelve Labours, also categorised as the second of the Non-Peloponnesian labours, Heracles was sent by King Eurystheus to steal the Mares from Diomedes. The mares’ madness was attributed to their unnatural diet which consisted of the flesh of unsuspecting guests or strangers to the island. Some versions of the myth say that the mares also expelled fire when they breathed. The Mares, which were the terror of Thrace, were kept tethered by iron chains to a bronze manger in the now vanished city of Tirida and were named Podargos, Lampon, Xanthos and Deinos. Although very similar, there are slight variances in the exact details regarding the mares’ capture. In one version, Heracles brought a number of volunteers to help him capture the giant horses. After overpowering Diomedes’ men, Heracles broke the chains that tethered the horses and drove the mares down to sea. Unaware that the mares were man-eating and uncontrollable, Heracles left them in the charge of his favored companion, Abderus, while he left to fight Diomedes. Upon his return, Heracles found that the boy was eaten. As revenge, Heracles fed Diomedes to his own horses and then founded Abdera next to the boy's tomb. In another version, Heracles, who was visiting the island, stayed awake so that he didn't have his throat cut by Diomedes in the night, and cut the chains binding the horses once everyone was asleep. Having scared the horses onto the high ground of a knoll, Heracles quickly dug a trench through the peninsula, filling it with water and thus flooding the low lying plain. When Diomedes and his men turned to flee, Heracles killed them with an axe, and fed Diomedes’ body to the horses to calm them. In yet another version, Heracles first captured Diomedes and fed him to the mares before releasing them. Only after realizing that their King was dead did his men, the Bistonians, attack Heracles. Upon seeing the mares charging at them, led in a chariot by Abderus, the Bistonians turned and fled. All versions have eating human flesh make the horses calmer, giving Heracles the opportunity to bind their mouths shut, and easily take them back to King Eurystheus, who dedicated the horses to Hera. In some versions, they were allowed to roam freely around Argos, having become permanently calm, but in others, Eurystheus ordered the horses taken to Olympus to be sacrificed to Zeus, but Zeus refused them, and sent wolves, lions, and bears to kill them. Roger Lancelyn Green states in his Tales of the Greek Heroes that the mares’ descendants were used in the Trojan War, and survived even to the time of Alexander the Great. After the incident, Eurystheus sent Heracles to bring back Hippolyta's Girdle.
Although not referred to directly as the Mares of Diomedes in the book, Diomedes himself is mentioned in chapter eight, and the horses, who are mentioned in chapters eight and nine, are described as both fire-breathing and flesh-eating.
