Xanthus (Ancient Greek: Ξανθός / Xanthós - " blond ") and Balius (Βαλιός / Baliós - " spotted ") were the immortal, talking horses of the Greek hero Achilles. They were sons of Zephyrus, the west wind, and the harpy Podarge.
Podarge was once grazing in horse-like form on the shores of the Ocean, when she was impregnated by Zephyrus. Hera endowed the horses with the ability to speak. Xanthus and Balius were given to Peleus, the father of Achilles, as wedding gifts.
In the Trojan War, when Patroclus was allowed to put on Achilles' armor to go to battle, he was also given Xanthus and Balius. On the battlefield, Patroclus was defeated and killed by the Trojan hero and prince Hector. Then the prodigious horses burst into tears.
They no longer responded to the exhortations of Automedon, Achilles' charioteer, and were unable to return to the Greek camp. Zeus took pity on them and arranged for Xanthus and Balius to return to the camp.
A little later, when Achilles was getting ready for battle, he reproached Xanthus and Balius for not bringing back alive his friend and comrade in arms Patroclus. Xanthus replied that they themselves could still bring Achilles back this time, but that he would die a short time later anyway.
These were Xanthus' last words, as the Erinyes silenced him. Achilles replied that he knew he was going to die soon, but that this did not stop him from seeking the heat of battle.