In April 323, Alexander the Great entered Babylon. The Chaldaeans, i.e., the famous astrologers working in the Esagila temple complex, came with warnings that he would die if he entered the city without due precautions.
Arrian of Nicomedia describes this his Anabasis, sections 7.16.5-17.5. They are given here in the translation by Aubrey de Sélincourt.
Alexander and the Chaldaeans
[7.16.5] On his march to Babylon, Alexander, after crossing the Tigris, was met by some Wise Men of the Chaldaeans, who drew him aside and begged him to go no further, because their god Bêlnote[The Greek name Belos is a translation of Akkadian Bêl, "lord", the title of the Babylonian supreme god Marduk, who was venerated in the Esagila.] had foretold that if he entered the city at that time, it would prove fatal to him.
[7.16.6] Alexander replied by quoting to them the line of [the playwright] Euripides: "Prophets are best who make the truest guess."
"My lord," said the Chaldaeans, "look not to the west;note[When he faced the west, Alexander would be looking to the setting sun (Appian of Alexandria, Civil wars, 2.153), the symbol of decline. Therefore, he was asked to enter the town through the Royal Gate in the west, where he had to face east. That, however, something happened near the eastern gate of Babylon, is confirmed by the cuneiform text that also mentions the death of Alexander (more...). Perhaps the setting sun was even more ominous to Alexander than the Babylonian astrologers knew. In 1977-1978, the royal tombs of Macedonia were excavated at Vergina, and the excavators discovered that there were many golden objects carrying a heraldic symbol, which they interpreted as a sixteen-pointed star and has often been called a star ever since. In fact, it is a sun; there are several ancient coins which show a (nearly) similar heraldic symbol, and in those cases, it is without any doubt a sun (e.g., the coins of Uranopolis). It should also be stressed that, according to legend, the founder of the Alexander's dynasty had been favored by the sun (Herodotus, Histories 8.137; text). The omen was therefore very bad indeed, because it referred to the Macedonian royal house. It should also be remembered that Alexander was the son of the Egyptian sun god Ra.] do not march westward with your army; but turn about and go eastward."
[7.16.7] But this was not easy for Alexander to do, as the country to the east was impracticable for troops. The truth was that fate was leading him to the spot where it was already written that he should die.
[7.17.1] Alexander had some suspicion that the Chaldaeans' attempt to prevent him from marching to Babylon on that occasion was not, in fact, based upon a prophecy of impending disaster at all; on the contrary, its object, he felt, might well be to secure their own advantage. In Babylon stood the great temple of Bêl, a huge edifice of baked bricks set in bitumen.note[The Esagila complex, dedicated to Marduk. One part of it was the Etemenanki, a tower 90 meters high (the "tower of Babel" from the Bible).]
[7.17.2] Like the other shrines in the city, it had been destroyed by Xerxes on his return from Greece,note[Xerxes returned from Greece in 479.] and Alexander had proposed to restore it.note[Alexander's rebuilding is mentioned in a cuneiform text, quoted here.]
According to some accounts, he intended to rebuild upon the original foundations, and for that reason the Babylonians had had instructions to clear the site. Others say he intended a still larger building than the old one.
[7.17.3] The workmen, however, once he was out of the way, dawdled over their job, so he proposed to set all his own troops to work upon it.
[7.17.4] Now a great deal of land and considerable treasure had been devoted by the Assyrian kings to the god Bêl, and from this the temple, in the old days, used to be maintained and the sacrifices offered to the god. But at the time of which I am speaking the Chaldaeans themselves had the disposal of the god's property, as there was nothing upon which the income could be spent. For these reasons it had occurred to Alexander that they night not want him to enter the city, lest the rebuilding of the temple might be rapidly completed and they, in consequence, lose the benefit of the money.
[7.17.5] Nevertheless, Aristobulus tells us that Alexander, so far as changing his direction was concerned, was ready to yield to their wishes; on the first day he halted his men on the Euphrates, and on the next advanced, keeping the river on his right hand, with the intention of first passing the western section of the city and then wheeling to the eastward.
[7.17.6] But it turned out that by this route the going was too bad for the army to get through, as anyone approaching the west side of the city and then turning east is bound to get bogged down in swampy land. The result was that Alexander disobeyed the divine command - half deliberately, and half because he could not help it.