John Gill, on Jer 51:23

Behold, I am against thee, O destroying mountain, saith the Lord, which destroyest all the earth,.... Babylon is called a mountain, though situated in a plain, because of its high walls, lofty towers, and hanging gardens, which made it look at a distance like a high mountain, as Lebanon, and others: or because it was a strong fortified city; so the Targum renders it, O destroying city: or because of its power and grandeur as a monarchy, it being usual to compare monarchies to mountains; see Isa 2:2; here called a "destroying" one for a reason given, because it destroyed all the earth, all the nations and kingdoms of it: the same character is given of mystical Babylon and its inhabitants, Rev 11:18, and I will stretch out mine hand upon thee: in a way of vindictive wrath, pouring it out upon her, and inflicting his judgments on her; laying hold on and seizing her in a furious manner, as a man does his enemy, when he has found him: and roll them down from the rocks; towers and fortresses in Babylon, which looked like rocks, but should be now demolished: and will make thee a burnt mountain: reduced to cinders and ashes by the conflagration of it: or, "a burning mountain": like Etna and Vesuvius; we never read of the burning of literal Babylon, but we do of mystical Babylon: see Rev 18:8; and with this compare Rev 8:8. The Targum renders it, a burnt city.