And, behold, here cometh a chariot of men, with a couple of horsemen. And he answered and said, Babylon is fallen, is fallen; and all the graven images of her gods he hath broken unto the ground.
Chariot of men - chariots with men in them; or rather, the same cavalcade or body of riders, horsemen two abreast, as in Isaiah 21:7 (Maurer). But Horsley, 'the man drawn in a car with a pair of riders.' The first half of this verse describes what the watchman sees; the second half, what the watchman says, in consequence of what he sees. In the interval between Isaiah 21:7; Isaiah 21:9, the overthrow of Babylon by the horsemen, or man in the car, is accomplished. The overthrow needed to be announced to the prophet by the watchman, owing to the great extent of the city. Herodotus (1: 131) says, that one part of the city was captured a considerable time before the other received the tidings of it.
And he answered - not to something said previously, but in reference to the subject in the mind of the writer, to be collected from the preceding discourse: proclaimeth (Job 3:2; margin, Daniel 2:26; Acts 5:8).
Babylon is fallen ... fallen. The repetition expresses emphasis and certainty (Psalms 92:9; Psalms 93:3: cf. Jeremiah 51:8; Revelation 18:2).
All the graven images of her gods he hath broken (and dashed) unto the ground - Bel, Merodach, etc. (Jeremiah 50:2; Jeremiah 51:44; Jeremiah 51:52). The Persians had no images, temples, or altars, and charged the makers of such with madness (Herodotus, 1: 131): therefore they dashed the Babylonian 'images broken unto the ground.'