Awaiting an evening of a national feast among Babylonians , 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 . 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 .