This land was eminently noted for metal mines, so that "its stones," in very many places, "were iron, and out of its hills was digged brass," Deuteronomy 8:9. From these gain accrued to the Jews: but to the Christians, not seldom slavery and misery; being frequently condemned hither by tyrants. So Eusebius of Edesius, "He was condemned to the metal mines of Palestine." And again, concerning others, "Then passing to the other confessors of Christ, he condemns them all to the brass mines, which were in Pheno of Palestine."
On the north part of the land, in the country of Asher, were mines of metal. Hence is that in Deuteronomy 33:25, "Thy shoes shall be iron and brass." On the south, in the desert of Sin, the utmost bounds of Judea, were mines also: hence -- and shall pass to Zin, as our translation reads, Numbers 34:4, -- in the Jerusalem Targumist, is over-against the mountain of iron: and in Jonathan, unto the palm-trees of the mountain of iron: and in the Talmudists, the palm-trees of the mountain of iron are fit to make a small bundle to carry in the hand in the feast of Tabernacles. On the east coast of Perea was also "an iron mountain," -- witness Josephus. And without doubt there were other such-like mines, scattered here and there in other parts of that land, though of them we have no mention.
You will not at all wonder at these underminings of the earth, seeing they brought so much profit and gain with them, and were so necessary to the life of man. But what shall we say of those dens and caves in rocks and mountains, whence no gain seemed to be digged, but rather danger arose to the neighbouring places oftentimes? For what were these, but lurking-places for wild beasts and robbers? There is infinite mention of these caves both in the Holy Scriptures and in other writings, especially in Josephus, where subterraneous passages, and dens, are mentioned a thousand times. And many of these were of a vast largeness, scarcely to be credited; those especially in the Talmudists, which are called "The dens of Zedekiah," not a few miles in distance.
But were those hollows the work of nature, or of the hands and industry of man? By one example, taken out of Josephus, the thing may be determined. Relating the story of a castle built by Hyrcanus in Perea, among other things he speaks thus: "Out of the rock against the mountain, having cut in two the prominent parts of it, he made dens of many furlongs long." And a little after, "He made the mouths that opened into these dens to be strait, that but one might go in at a time, and no more": "and this he did on purpose for security's sake, and for avoiding danger, in case he should be besieged by his brethren."
These dens, therefore, were cut out of mountains and rocks for the uses of war, that they might serve for refuge and strength. And it is probable the Canaanites, a warlike and gigantic nation, had digged very many of these caves before the entrance of the Israelites into that land; and that the Israelites also increased the number of them. See concerning these caves, Joshua 10:16; Judges 6:2; 1 Samuel 22:1, and 24:3; 1 Kings 18:13; Isaiah 2:19, &c.