John Calvin Commentary Jeremiah 51:30

"The mighty men of Babylon have forborne to fight, they remain in their strongholds; their might hath failed; they are become as women: her dwelling-places are set on fire; her bars are broken." — Jeremiah 51:30 (ASV)

The Prophet shows here, as if pointing with a finger, the manner of the destruction of Babylon, such as it is described by pagan authors. He then says that the valiant men of Babylon, even those who had been chosen to defend the city, ceased to fight. For the city was taken more by craft than by open force; after a long siege, Cyrus was ridiculed by the Babylonians, and then they confidently held a feast.

In the meantime, two of Belshazzar's eunuchs defected to Cyrus. For, as Xenophon relates, the tyrant had slain the son of one and castrated the other as a mark of disgrace. This is why they revolted from him, and Cyrus was instructed by them how he could take the city. The fords were dried up when Belshazzar suspected nothing of the sort, and during the night, he heard that the city was taken. Daniel gives a clearer description, for he says that a regular feast was being held, that the hand of a writer appeared on the wall, and that the king, terrified, heard from Daniel that the end of his kingdom was near and that the city was taken that very night (Daniel 5:25–30). Therefore, the Prophet now says that the valiant men stopped, so that they did not fight. He is indeed speaking of what was future, but we know the way of the prophets, for they related what was to come as though it had already taken place.

Afterwards, he adds that they sat down in their fortresses, for the city was not taken by storm—there was no fighting. Instead, the forces passed silently through the fords, and the soldiers entered the middle of the city. The king was slain along with all his satraps, and then all parts of the city were seized. We now see, then, that the Spirit of God spoke by the mouth of Jeremiah, as if about a thing that had already taken place.

He then adds that their valor had failed or languished, because terror stupefied them when they heard that the city was taken. So too, what is added became true: that they became women, meaning they were like women in courage, for no one dared to oppose the conquerors. Fighting might still have been carried on by such a large multitude; indeed, they might have engaged their enemies in hundreds or thousands of the city streets, for it would have been easy to attack them in the night. But the Prophet says that they all became like women in courage. At last, he adds that burnt by enemies were the palaces and that the bars of the gates were broken, for no one dared to call to arms after they heard that the city was taken.