Charles Ellicott Commentary Isaiah 21:9

"and, behold, here cometh a troop of men, horsemen in pairs. And he answered and said, Fallen, fallen is Babylon; and all the graven images of her gods are broken unto the ground." — Isaiah 21:9 (ASV)

And, behold, here cometh ... —Better, Behold, there came ... The words narrate a second vision, not the watchman’s narrative of the first. He sees now, as it were, a part of the cavalcade which he had seen before, and now it is no longer silent, but reports what has been accomplished. Babylon is fallen, is fallen! The words are applied to the destruction of the mystical Babylon in Revelation 14:8; Revelation 18:2. Stress is laid on the destruction of the idols of Babylon by the iconoclastic Persians.