What river did Cyrus the Great divert to capture Babylon?

Cyrus the Great is traditionally said to have diverted the Euphrates to capture Babylon.

In 539 BC, Cyrus’s Achaemenid Persian army conquered Babylon, the capital of the Neo-Babylonian Empire. Herodotus and Xenophon describe a plan in which Persian forces redirected the Euphrates into channels or trenches, lowering the water level enough for soldiers to enter through the riverbed. Babylon was reportedly celebrating a festival, helping the attackers achieve surprise.

The story explains how an apparently formidable city could fall so quickly, but its exact historical details are debated. The Babylonian Chronicle confirms that Babylon was captured by Cyrus, yet it does not describe the dramatic river diversion in the same way. Some modern reconstructions suggest Persian troops entered through a gate or used existing waterways, while later Greek accounts may have elaborated the episode.

The Euphrates ran through Babylon and was integrated into the city’s defenses and daily life. That makes it the river central to the traditional account; the Tigris, another major Mesopotamian river, is the common distractor.