Xanthus and Balius are the two immortal horses that Poseidon gave to Peleus as a wedding present. The horses were the offspring of Zephyrus, the west wind, (or Zeus) and the Harpy Podarge. They served as chariot horses for Achilles during the Trojan War. When he rebuked them for permitting Patroclus to be killed, Xanthos reproved Achilles by saying that a god had slain Patroclus and that a god would soon kill him too. After thus prophesying, the horse was struck dumb by the Erinyes.