The twelfth and last labor of Hercules was to bring from Hades the three-headed dog, Cerberus. With the help of Mercury and Minerva, he descended into the dread realm of Pluto, and begged that grim monarch to let him take Cerberus into the upper world. Pluto was not willing at first to lose the guardian of his gates even for a short time; but at length he consented to let Hercules do as he desired on condition that Cerberus should not be bound or any weapons used upon him. So the fierce three-headed creature was carried, snarling and struggling, in the hero's strong arms; and when the pair approached the throne of Eurystheus, the horror-struck monarch implored Hercules to take the monster back as quickly as possible, for the sight of its dripping jaws, from which oozed the deadly nightshade, so terrified Eurystheus that he sought refuge in a huge jar, and would not come out until his courtiers assured him that Cerberus was safely out of the country. When the twelve labors were ended, Hercules's term of service at the court of Eurystheus was over, and he was free to wander where he willed. He spent many years roaming through various lands and assisting other heroes who, like himself, were in search of adventures. He took part in the battle between the Centaurs and Lapithæ;[82] joined in the Argonautic expedition; organized the first siege of Troy, and braved the terrors of Hades to bring Alcestis back to her repentant husband.[83] The expedition against Troy was one of revenge, for the false Laomedon had never paid the gold that he had promised for the release of his daughter Hesione from the sea-monster; and Hercules now set out to punish the treacherous king.[84] So he sailed for Troy with eighteen ships, and the city fell into his hands with but little resistance. Laomedon was killed, his son Priam placed on the throne of Troy, and Hesione given in marriage to Telamon, one of the Greeks who accompanied Hercules. [Illustration: Hercules serving Omphale]