John Gill Bible Commentary

Set up the standard upon the walls of Babylon,.... This is not said to the Medes and Persians, to put up a flag on the walls of Babylon, as a sign of victory, as Kimchi, Abarbinel, and others think; for as yet the city is not supposed to be taken by what follows; but rather to the Babylonians, to set up an ensign on their walls, to gather the inhabitants together, to defend their city, and the bulwarks of it; which, with what follows, is ironically spoken: make the watch strong; to guard the city; observe the motions of the enemy, and give proper and timely notice; increase and double it: set up watchmen; meaning the keepers of the walls; place them upon them, to keep a good look out, that they might not be surprised: this seems to respect the great carelessness and security the whole city was in the night it was taken; being wholly engaged in feasting and revelling, in rioting and drunkenness, having no fear of danger, or concern for their safety; with which they are tacitly upbraided: prepare the ambushes; or, "liers in wait" (p); to second or relieve those on the walls upon occasion; or seize unawares the besiegers, should they attempt to scale the walls, and enter the city: for the Lord hath devised and done that which he spoke against the inhabitants of Babylon; or as he hath devised, so hath he done, or will do: his purposes cannot be frustrated, his counsel shall stand; and therefore had the Babylonians been ever so industrious in their own defence, they could never have prevented their ruin and destruction, which was resolved upon, and accordingly effected. (p) "insidiatores", Montanus, Junius & Tremellius, Piscator, Cocceius, Schmidt.