Phineus had been blinded by Neptune, as a punishment for having shown Phryxus the way to Colchis. He was also tormented by the harpies, frightful winged monsters, who flew down from the clouds whenever he attempted to eat, snatched the food from his lips, and left on it such a vile odor that no man could come near it. He, being a prophet, knew that the Argonauts would free him from this curse. There were with them Zetes and Calias, winged sons of Boreas, the god of the north winds; and when the harpies descended again to spoil the prophet's meal, these winged warriors not only drove them away, but pursued them through the air. They could not overtake them, but the harpies were forbidden by Jupiter to molest Phineus any longer. The blind prophet, grateful for this deliverance, told the voyagers how they might escape a dreadful danger which lay in their onward way. This came from the Symplegades, two rocks between which their ships must pass, and which continually opened and closed, with a violent collision, and so swiftly that even a bird could scarce fly through the opening in safety. When the Argo reached the dangerous spot, at the suggestion of Phineus, a dove was let loose. It flew with all speed through the opening, but the rocks clashed together so quickly behind it that it lost a few feathers of its tail. Now was their opportunity. The rowers dashed their ready oars into the water, shot forward with rapid speed, and passed safely through, only losing the ornaments at the stern of their ship. Their escape, however, they owed to the goddess Minerva, whose strong hand held the rocks asunder during the brief interval of their passage. It had been decreed by the gods that if any ship escaped these dreadful rocks they should forever cease to move. The escape of the Argo fulfilled this decree, and the Symplegades have ever since remained immovable. Onward went the daring voyagers, passing in their journey Mount Caucasus, on whose bare rock Prometheus, for the crime of giving fire to mankind, was chained, while an eagle devoured his liver. The adventurers saw this dread eagle and heard the groans of the sufferer himself. Helpless to release him whom the gods had condemned, they rowed rapidly away. Finally Colchis was reached, a land then ruled over by King AEetes, from whom the heroes demanded the golden fleece, stating that they had been sent thither by the gods themselves. AEetes heard their request with anger, and told them that if they wanted the fleece they could have it on one condition only. He possessed two fierce and tameless bulls, with brazen feet and fire-breathing nostrils. These had been the gift of the god Vulcan. Jason was told that if he wished to prove his descent from the gods and their sanction of his voyage, he must harness these terrible animals, plough with them a large field, and sow it with dragons' teeth.