Adam Clarke on Jeremiah 50:24

I have laid a snare for thee - It was not by storm that Cyrus took the city. The Euphrates ran through it; he dug a channel for the river in another direction, to divert its stream; he waited for that time in which the inhabitants had delivered themselves up to debauchery: in the dead of the night he turned off the stream, and he and his army entered by the old channel, now void of its waters. This was the snare of which the prophet here speaks. See Nerodotus, lib. i., c. 191.