By the gates of the rivers the Prophet means that part of the city which was most fortified by the river Tigris; for the Tigris flowed close by the city. As then the Tigris was like the strongest defense, (for we know it to have been a most rapid river,) the Prophet ridicules the confidence of the Ninevites, who thought that the access of enemies could be wholly prevented in that part where the Tigris flowed. The gates then of the rivers are opened; that is, your river shall not prevent your enemies from breaking through and penetrating into your city. We hence see, that the Prophet removes all the hindrances which might have seemed available to keep off enemies; and he did so, not so much for the sake of Nineveh as for the sake of his chosen people, that the Israelites and Jews might know, that that city was no less in the power of God than any other; for God can no less easily pass through rivers than go along the plain, where there is no obstacle. We now see why the Prophet says, that the gates of the rivers were opened: and then he adds, The palace is dissolved; that is, there will be no impediment to prevent the approach of enemies; for all the fortresses will melt away, and that of themselves, as though they were walls of paper, and the stones, as though they were water. He afterwards adds --

The gates of the rivers shall be opened, and the palace shall be disolved - All gives way in an instant at the will of God; the strife is hushed; no more is said of war and death; there is no more resistance or bloodshed; no sound except the wailing of the captives, the flight of those who can escape, while the conquerors empty it of the spoil, and then she is left a waste. The swelling of the river and the opening made by it may have given rise to the traditional account of Ctesias, although obviously exaggerated as to the destruction of the wall. The exaggerated character of that tradition is not inconsistent with, it rather implies, a basis of truth. It is inconceivable that it should have been thought, that walls, of the thickness which Ctesias had described, were overthrown by the swelling of any river, unless some such event as Ctesias relates, that the siege was ended by an entrance afforded to the enemy through some bursting in of the river, had been true.
Nahum speaks nothing of the wall, but simply of the opening of "the gates of the river," obviously the gates, by which the inhabitants could have access to the rivers , which otherwise would be useless to them except as a wall. These "rivers" correspond to the "rivers," the artificial divisions of the Nile, by which No or Thebes was defended, or "the rivers of Babylon" Psalm 137:1 which yet was washed by the one stream, the Euphrates. But Nineveh was surrounded and guarded by actual rivers, the Tigris and the Khausser, and, (assuming those larger dimensions of Nineveh, which are supported by evidences so various ) the greater Zab, which was "called the frantic Zab on account of the violence of its current." "The Zab contained (says Ainsworth ), when we saw it, a larger body of water than the Tigris, whose tributaries are not supplied by so many snow-mountains as those of the Zab." Of these, if the Tigris be now on a level lower than the rains of Nineveh, it may not have been so formerly.
The Khausser, in its natural direction, ran through Nineveh where, now as of old, it turns a mill, and must, of necessity, have been fenced by gates; else any invader might enter at will: as, in modern times, Mosul has its "gate of the bridge." A break in these would obviously let in an enemy, and might the more paralyze the inhabitants, if they had any tradition, that the river alone could or would be their enemy, as Nahum himself prophesied. Subsequently inaccuracy or exaggeration might easily represent this to be an overthrow of the walls themselves. It was all one, in which way the breach was made.
The palace shall be dissolved - The prophet unites the beginning and the end. The river-gates were opened; what had been the fence against the enemy became an entrance for them: with the river, there poured in also the tide of the people of the enemy. The palace, then, the imperial abode, the center of the empire, embellished with the history of its triumphs, sank, was disolved , and ceased to be. It is not a physical loosening of the sun-dried bricks by the stream which would usually flow harmless by; but the dissolution of the empire itself. : "The temple, that is, his kingdom was destroyed." The palaces both of Khorsabad and Kouyunjik lay near the Khausser and both bear the marks of fire .

The gates of the rivers shall be opened - I have already referred to this, see the note on Nahum 1:8; but it will be necessary to be more particular. The account given by Diodorus Siculus, lib. ii., is very surprising. He begins thus: Ην δ' αυτῳ λογιον παραδεδομενον εκ προγονων, κ.τ.λ. - "There was a prophecy received from their forefathers, that Nineveh should not be taken till the river first became an enemy to the city. It happened in the third year of the siege, that the Euphrates [query, Tigris] being swollen with continued rains, overflowed part of the city, and threw down twenty stadia of the wall. The king then imagining that the oracle was accomplished, and that the river was now manifestly become an enemy to the city, casting aside all hope of safety, and lest he should fall into the hands of the enemy, built a large funeral pyre in the palace, (εν τοις βασιλειοις), and having collected all his gold and silver and royal vestments, together with his concubines and eunuchs, placed himself with them in a little apartment built in the pyre; burnt them, himself, and the palace together. When the death of the king (Sardanapalus) was announced by certain deserters, the enemy entered in by the breach which the waters had made, and took the city." Thus the prophecy of Nahum was literally fulfilled:" the gates of the river were opened, and the palace dissolved," i.e., burnt.

The gates of the rivers shall be opened,.... Of Diava and Adiava, or Lycus and Caprus, between which, according to some writers (i), Nineveh was situated; or the gates of the city, which lay nearest to the river Tigris, are meant; or that river itself, the plural for the singular, which overflowing, broke down the walls of the city for two and a half miles, and opened a way for the Medes and Chaldeans to enter in; of which see Nahum 1:8,
and the palace shall be dissolved; by the inundation, or destroyed by the enemy; meaning the palace of the king, which might be situated near the river; or the temple of Nisroch the Assyrian deity, or Jupiter Belus; for the same word (k) signifies a temple as well as palace.
(i) Vid. Fuller. Miscel. Sacr. l. 3. c. 6. (k) "templum", V. L. Junius & Tremellius, Piscator, Drusius, Cocceius.

The gates of the rivers . . . opened--The river wall on the Tigris (the west defense of Nineveh) was 4,530 yards long. On the north, south, and east sides, there were large moats, capable of being easily filled with water from the Khosru. Traces of dams ("gates," or sluices) for regulating the supply are still visible, so that the whole city could be surrounded with a water barrier (Nahum 2:8). Besides, on the east, the weakest side, it was further protected by a lofty double rampart with a moat two hundred feet wide between its two parts, cut in the rocky ground. The moats or canals, flooded by the Ninevites before the siege to repel the foe, were made a dry bed to march into the city, by the foe turning the waters into a different channel: as Cyrus did in the siege of Babylon [MAURER]. In the earlier capture of Nineveh by Arbaces the Mede, and Belesis the Babylonian, DIODORUS SICULUS, [1.2.80], states that there was an old prophecy that it should not be taken till the river became its enemy; so in the third year of the siege, the river by a flood broke down the walls twenty furlongs, and the king thereupon burnt himself and his palace and all his concubines and wealth together, and the enemy entered by the breach in the wall. Fire and water were doubtless the means of the second destruction here foretold, as of the first.
dissolved--by the inundation [HENDERSON]. Or, those in the palace shall melt with fear, namely, the king and his nobles [GROTIUS].

The gates - Of the city toward the river. The rivers - Of the Tigris, upon which Nineveh stood. Dissolved - While the Chaldeans besieged Nineveh, a mighty deluge overthrew the walls of Nineveh, by the space of twenty furlongs, through which breach the besiegers made their entrance. Dissolved - As if melted, it shall drop to pieces.