In the Twelve Labors of Hercules, what did the Mares of Diomedes eat?

In the Twelve Labors of Hercules, the Mares of Diomedes ate human flesh.

The mares belonged to Diomedes, king of the Bistones in Thrace. They were described as wild, dangerous horses that were fed human beings. Hercules was ordered to capture them during his eighth labor and bring them to Eurystheus.

In a widely told version, Hercules first brought the horses under control and then fed Diomedes to his own mares. After eating their master, the animals became calm enough to handle. Hercules then completed the journey with them.

The story is sometimes confused with the labor involving Geryon’s cattle, because both involve transporting dangerous animals over long distances. The mares’ defining feature, however, is their cannibalistic diet, not fire-breathing or supernatural speed.