'Strongholds' in the Bible

And they put him in a cage with hooks, and brought him to the king of Babylon; they brought him into strongholds, that his voice should no more be heard upon the mountains of Israel.

Thus shalt thou say unto them, Thus saith the Lord Jehovah: As I live, surely they that are in the waste places shall fall by the sword; and him that is in the open field will I give to the beasts to be devoured; and they that are in the strongholds and in the caves shall die of the pestilence.