Cyrus the Great of Persia entered Babylon after his general Ugbaru had already taken the city, reportedly diverting the Euphrates to allow troops to march along the riverbed and through unguarded gates. The bloodless conquest ended Nabonidus's reign and the Neo-Babylonian Empire, and Cyrus's subsequent decree allowing exiled peoples, including Jews held captive since Nebuchadnezzar's conquest, to return home became a landmark act of ancient statecraft.
According to the Nabonidus Chronicle and later Greek historians, Babylon fell to the Persian army with startling ease. King Nabonidus was away from the city, and popular resentment against him, partly for neglecting the cult of Marduk, meant the population offered little resistance when Cyrus's forces arrived.
Herodotus later told a dramatic version in which Persian engineers diverted the Euphrates River, lowering its level enough for soldiers to wade into the city along the riverbed while Babylonians celebrated a festival, unaware their gates stood open. Whether or not the story is precisely true, the city's fall was swift and remarkably bloodless, a stark contrast to the region's usual conquest narratives.
Cyrus entered as a liberator rather than a destroyer. He presented himself as chosen by Marduk to restore proper worship, and issued a proclamation, later echoed in the biblical Book of Ezra, permitting deported peoples, including the Judean exiles taken decades earlier by Nebuchadnezzar II, to return to their homelands and rebuild their temples. This act of policy, inscribed on the Cyrus Cylinder, is often cited as an early charter of religious tolerance and remains one of antiquity's most consequential political decisions.