Cyrus’ sack of Babylon in 539 BCE was a truly impressive feat. Here’s how Wikipedia describes it:
In 539 BC, the Neo-Babylonian Empire fell to Cyrus the Great, king of Persia, with an unprecedented military engagement known as the Battle of Opis. The famed walls of Babylon were indeed impenetrable, with the only way into the city through one of its many gates or through the Euphrates, which ebbed beneath its thick walls. Metal gates at the river’s in-flow and out-flow prevented underwater intruders, if one could hold one’s breath to reach them. Cyrus (or his generals) devised a plan to use the Euphrates as the mode of entry to the city, ordering large camps of troops at each point and instructed them to wait for the signal. Awaiting an evening of a national feast among Babylonians (generally thought to refer to the feast of Belshazzar mentioned in Daniel V), Cyrus’ troops diverted the Euphrates river upstream, causing the Euphrates to drop to about ‘mid thigh level on a man’ or to dry up altogether. The soldiers marched under the walls through the lowered water. The Persian Army conquered the outlying areas of the city’s interior while a majority of Babylonians at the city center were oblivious to the breach. The account was elaborated upon by Herodotus [1.191], and is also mentioned by passages in the Hebrew Bible [Isa 44:9-45:4; Jer 50-51].
For your reading pleasure, here are links to the three ancient works the Wikipedia article cites, with excerpts to whet your appetite.
. . . and when he came to the lake, Cyrus dealt with it and with the river just as had the Babylonian queen: drawing off the river by a canal into the lake, which was a marsh, he made the stream sink until its former channel could be forded. . . . because of the great size of the city (those who dwell there say) those in the outer parts of it were overcome, but the inhabitants of the middle part knew nothing of it; all this time they were dancing and celebrating a holiday which happened to fall then, until they learned the truth only too well.
I am the Lord, who made all things, who alone stretched out the heavens, who by myself spread out the earth; who frustrates the omens of liars, and makes fools of diviners; . . . who says to the deep, “Be dry— I will dry up your rivers”; who says of Cyrus, “He is my shepherd, and he shall carry out all my purpose.”
Declare among the nations and proclaim,
set up a banner and proclaim,
do not conceal it, say:
Babylon is taken,
Bel is put to shame,
Merodach is dismayed.
Her images are put to shame,
her idols are dismayed.
For out of the north a nation has come up against her; it shall make her land a desolation, and no one shall live in it; both human beings and animals shall flee away.
I especially enjoy the reference in Isaiah, because it comes at the end of a very funny satire on idolatry, when compared with Yahweh worship. I also think it’s very cool that an event recorded in a Greek historian was of such significance for Israel that it made its way into two of the prophets.