The fourth labor to which Hercules lent his great strength was the killing of a wild boar that haunted Mount Erymanthus in Arcadia. While on this expedition, the hero was attacked by the centaurs, and when he shot at them with his poisoned arrows, one of the deadly missiles flew far and struck his loved tutor Chiron, who was galloping toward the combatants, hoping to settle the quarrel peaceably. When Hercules saw Chiron fall, he rushed to his side and tried to stanch the fatal wound; but the dying centaur knew that his end had come, and sorrowfully bade the hero farewell. To reward Chiron for his long service, the gods transferred him to the heavens as the constellation Sagittarius. Hercules was next sent to kill the flock of fierce birds whose cruel beaks and sharp talons made havoc in the country around Lake Stymphalus. The foul mist that rose from the stagnant water over which the birds hovered was so deadly to breathe that Hercules could hardly approach the lake; but with the help of his poisoned arrows he was able to wound the birds at a distance. After hours spent in this pestilent atmosphere he killed the entire flock and returned to the court of Eurystheus to report his success. The most unpleasant of all Hercules's labors was the cleaning of the stables where Augeas, king of Elis, kept his herd of a thousand oxen. These stables had not been cleaned for thirty years; and when Hercules caught one glimpse of the filth within them, he felt that this was too degrading a task for him to undertake. But the work had to be done; and since he could not put his hand to anything so foul, he looked about for some other means to accomplish the labor. Not far from the stables flowed two rivers, the Peneus and Alpheus, and these Hercules turned out of their courses and made them rush through the filthy building until every part of the stables of Augeas was washed perfectly clean. Then he restored the rivers to their former beds, and returned home to report this task fulfilled. The next labor that was assigned to the hero was the capture of a mad bull given by Neptune to King Minos. In the early days of his power, Minos had boasted that he could obtain anything that he wished from the gods; and had accordingly begged of Neptune a bull for the sacrifices. The kindly sea-god sent a splendid offering, but when Minos saw the bull's size and beauty, he resolved to keep it. So he substituted another animal for the sacrifices. This angered Neptune so much that he made the bull go mad; and it rushed here and there over the island, causing great terror among the people. The creature was finally caught and overcome by Hercules, who rode it through the waves to Greece. The offspring of this bull was the famous Minotaur which the hero Theseus pursued through its labyrinth, and slew.