After these transactions, Alexander was seized by an ardent desire to visit Ammon[360] in Libya, partly in order to consult the god, because the oracle of Ammon was said to be exact in its information, and Perseus and Heracles were said to have consulted it, the former when he was despatched by Polydectes[361] against the Gorgons, and the latter, when he visited Antaeus[362] in Libya and Busiris[363] in Egypt. Alexander was also partly urged by a desire of emulating Perseus and Heracles, from both of whom he traced his descent.[364] He also deduced his pedigree from Ammon, just as the legends traced that of Heracles and Perseus to Zeus. Accordingly he made the expedition to Ammon with the design of learning his own origin more certainly, or at least that he might be able to say that he had learned it. According to Aristobulus, he advanced along the seashore to Paraetonium through a country which was a desert, but not destitute of water, a distance of about 1,600 stades.[365] Thence he turned into the interior, where the oracle of Ammon was located. The route is desert, and most of it is sand and destitute of water. But there was a copious supply of rain for Alexander, a thing which was attributed to the influence of the deity; as was also the following occurrence. Whenever a south wind blows in that district, it heaps up the sand upon the route far and wide, rendering the tracks of the road invisible, so that it is impossible to discover where one ought to direct one’s course in the sand, just as if one were at sea; for there are no landmarks along the road, neither mountain anywhere, nor tree, nor permanent hill standing erect, by which travellers might be able to form a conjecture of the right course, as sailors do by the stars.[366] Consequently, Alexander’s army lost the way, and even the guides were in doubt about the course to take. Ptolemy, son of Lagus, says that two serpents went in front of the army, uttering a voice, and Alexander ordered the guides to follow them, trusting in the divine portent. He says too that they showed the way to the oracle and back again. But Aristobulus, whose account is generally admitted as correct, says that two ravens flew in front of the army, and that these acted as Alexander’s guides. I am able to assert with confidence that some divine assistance was afforded him, for probability also coincides with the supposition; but the discrepancies in the details of the various narratives have deprived the story of certainty.[367] CHAPTER IV. THE OASIS OF AMMON.