The River Halys, a great river of Asia Minor, which flows northward into the Black Sea, was the eastern boundary of the Lydian empire. Croesus began to entertain the design of raising an army and crossing the Halys, to invade the empire of Cyrus, thinking that that would perhaps be safer policy than to wait for Cyrus to cross the Halys, and bring the war upon him. Still, the enterprise of invading Persia was a vast undertaking, and the responsibility great of being the aggressor in the contest. After carefully considering the subject in all its aspects, Croesus found himself still perplexed and undecided. The Greeks had a method of looking into futurity, and of ascertaining, as they imagined, by supernatural means, the course of future events, which was peculiar to that people; at least no other nation seems ever to have practiced it in the precise form which prevailed among them. It was by means of the oracles. There were four or five localities in the Grecian countries which possessed, as the people thought, the property of inspiring persons who visited them, or of giving to some natural object certain supernatural powers by which future events could be foretold. The three most important of these oracles were situated respectively at Delphi, at Dodona, and at the Oasis of Jupiter Ammon. Delphi was a small town built in a sort of valley, shaped like an amphitheater, on the southern side of Mount Parnassus. Mount Parnassus is north of the Peloponnesus, not very far from the shores of the Gulf of Corinth. Delphi was in a picturesque and romantic situation, with the mountain behind it, and steep, precipitous rocks descending to the level country before. These precipices answered instead of walls to defend the temple and the town. In very early times a cavern or fissure in the rocks was discovered at Delphi, from which there issued a stream of gaseous vapor, which produced strange effects on those who inhaled it. It was supposed to inspire them. People resorted to the place to obtain the benefit of these inspirations, and of the knowledge which they imagined they could obtain by means of them. Finally, a temple was built, and a priestess resided constantly in it, to inhale the vapor and give the responses. When she gave her answers to those who came to consult the oracle, she sat upon a sort of three-legged stool, which was called the sacred tripod. These stools were greatly celebrated as a very important part of the sacred apparatus of the place. This oracle became at last so renowned, that the greatest potentates, and even kings, came from great distances to consult it, and they made very rich and costly presents at the shrine when they came. These presents, it was supposed, tended to induce the god who presided over the oracle to give to those who made them favorable and auspicious replies. The deity that dictated the predictions of this oracle was Apollo.