The Mares of King Diomedes - The 10th Labor of Hercules

The mares were horses. The mares were fed on human flesh. Hercules knew he needed help to capture these fearsome animals. Together with some good friends he had made on his travels, Hercules and his band of volunteers journeyed to the land of Thrace.
The mares were gentle. That surprised Hercules. He led one out of the stable. The other mares followed. Things were moving along nicely when Hercules was attacked by King Diomedes and the king's men. In the heat of battle, the king was thrown from his horse. His horse ate him.
When the king's men saw what had happened, they jumped from their horses and ran away. The mares ran after them. Hercules quickly gathered up the fleeing animals. With the help of his volunteers, Hercules muzzled the mares, then led them to King Eury.