Charles Ellicott Commentary Jeremiah 51:12

"Set up a standard against the walls of Babylon, make the watch strong, set the watchmen, prepare the ambushes; for Jehovah hath both purposed and done that which he spake concerning the inhabitants of Babylon." — Jeremiah 51:12 (ASV)

Set up the standard upon the walls of Babylon. —The Authorised version, following the Septuagint and the Vulgate, takes the words as an ironical summons to a defence which will prove fruitless. The preposition for “upon” may, however, mean against, and this agrees better with the context. The “standards” are the banners or signals that direct an attack on a given point of the walls. The “watch” and “watchmen” are the scouts and sentinels placed to give notice of any attempt at a sally on the part of the besieged. The “ambush” may indicate generally any sudden attack, or, more specifically, the stratagem of a feigned flight, like that employed by Joshua in the attack on Ai (Joshua 8:14–16).