Diomedes was a king of the Bistonians, a Thracian people known for their savagery who lived around Lake Bistonis. The son of Ares and either the nymph Cyrene or Asteria, daughter of Atlas, and the husband of Hippodamia, he is not to be confused with the Diomedes who took part in the Trojan War. This Diomedes had four savage mares which fed on human flesh and which he loosed against strangers entering his kingdom. Because they were so fierce they were kept tethered with iron chains, and guards were permanently posted around their stable. The eighth of the twelve labours that Eurystheus imposed upon Heracles was to put an end to this terrible practice and bring the mares back to Mycenae. According to Apollodorus, Heracles set off with a band of volunteers, among them his friend Abderus, son of Hermes and Thronia and a native of Opus, in Locris. Upon arriving at Diomedes’ stables, Heracles overpowered the grooms and led the mares away. When the local people learned of this, however, they attacked him in order to recover the animals. Heracles entrusted the mares to Abderus, but they were too strong for him and killed him. Having defeated his attackers, Heracles then slew Diomedes and in memory of his friend founded the city of Abdera in the place where he had died, ordering that games be held annually in his honor. He then took the mares to Eurystheus, who dedicated them to Hera or, by another account, set them free on Mount Olympus where they were devoured by wild beasts. Yet another version of the myth says that Heracles killed Diomedes by feeding him to his own mares.
