In October 539 BCE, the Persian king Cyrus took Babylon, the ancient capital of an empire covering modern Iraq, Syria, Lebanon, and Israel. In a broader sense, Babylon was the ancient world's capital of scholarship and science. The subject provinces soon recognized Cyrus as their legitimate ruler. Since he was already lord of peripheral regions in modern Turkey and Iran (and Afghanistan?), it is not exaggerated to say that the conquest of Babylonia meant the birth of a true world empire. The Achaemenid Empire was to last for more than two centuries, until it was divided by the successors of the Macedonian king Alexander the Great. A remarkable aspect of the capture of Babylon is the fact that Cyrus allowed the Jews (who were exiled in Babylonia) to return home.
The Histories by the Greek researcher Herodotus of Halicarnassus (fifth century BCE) are the world's first historical study. The account of the Fall of Babylon - which is here presented in the translation by George Rawlinson - proves beyond all reasonable doubt that the author never talked to a Babylonian about the event and never visited the city. He has only two details right: that Cyrus entered Babylonia at Opis, where a battle was fought, and that captured the ancient city.
Herodotus on Cyrus' capture of Babylon
[1.189] Cyrus on his way to Babylon came to the banks of the Gyndes,note[The Diyala.] a stream which, rising in the Matienian mountains, runs through the country of the Dardanians, and empties itself into the river Tigris. The Tigris, after receiving the Gyndes, flows on by the city of Opis, and discharges its waters into the Erythraean sea.note[I.e., the Persian Gulf.] When Cyrus reached this stream, which could only be passed in boats, one of the sacred white horses accompanying his march, full of spirit and high mettle, walked into the water, and tried to cross by himself; but the current seized him, swept him along with it, and drowned him in its depths. Cyrus, enraged at the insolence of the river, threatened so to break its strength that in future even women should cross it easily without wetting their knees. Accordingly he put off for a time his attack on Babylon, and, dividing his army into two parts, he marked out by ropes one hundred and eighty trenches on each side of the Gyndes, leading off from it in all directions, and setting his army to dig, some on one side of the river, some on the other, he accomplished his threat by the aid of so great a number of hands, but not without losing thereby the whole summer season.
[1.190] Having, however, thus wreaked his vengeance on the Gyndes, by dispersing it through three hundred and sixty channels, Cyrus, with the first approach of the ensuing spring, marched forward against Babylon. The Babylonians, encamped without their walls, awaited his coming. A battle was fought at a short distance from the city, in which the Babylonians were defeated by the Persian king, whereupon they withdrew within their defenses. Here they shut themselves up, and made light of his siege, having laid in a store of provisions for many years in preparation against this attack; for when they saw Cyrus conquering nation after nation, they were convinced that he would never stop, and that their turn would come at last.
[1.191] Cyrus was now reduced to great perplexity, as time went on and he made no progress against the place. In this distress either some one made the suggestion to him, or he bethought himself of a plan, which he proceeded to put in execution. He placed a portion of his army at the point where the river enters the city, and another body at the back of the place where it issues forth, with orders to march into the town by the bed of the stream, as soon as the water became shallow enough: he then himself drew off with the unwarlike portion of his host, and made for the place where Nitocrisnote[A legendary former queen.] dug the basin for the river, where he did exactly what she had done formerly: he turned the Euphrates by a canal into the basin, which was then a marsh, on which the river sank to such an extent that the natural bed of the stream became fordable.
Hereupon the Persians who had been left for the purpose at Babylon by the, river-side, entered the stream, which had now sunk so as to reach about midway up a man's thigh, and thus got into the town. Had the Babylonians been apprised of what Cyrus was about, or had they noticed their danger, they would never have allowed the Persians to enter the city, but would have destroyed them utterly; for they would have made fast all the street gates which gave access to the river, and mounting upon the walls along both sides of the stream, would so have caught the enemy, as it were, in a trap. But, as it was, the Persians came upon them by surprise and so took the city. Owing to the vast size of the place, the inhabitants of the central parts (as the residents at Babylon declare) long after the outer portions of the town were taken, knew nothing of what had chanced, but as they were engaged in a festival, continued dancing and reveling until they learnt about the capture. Such, then, were the circumstances of the first taking of Babylon.