Joshua 15:8

and the border went up From En-rogel the border went up into the valley of the son of Hinnom, on the south side of the Jebusite, that is Jerusalem. The direction accordingly runs S. S. W. of Jerusalem, where the valley mentioned lies. Nothing is known of this Hinnom. Possibly he was some ancient hero, who had encamped here, and from whom it was called "Ge-Ben-Hinnom," "the Ravine of the son of Hinnom," whence came "Ge-Hinnom," and so "Gehenna." It is a deep retired glen, shut in by rugged cliffs, with the bleak mountain-sides rising over all. Here (a) Solomon erected high places for Moloch (1 Kings 11:7), and (b) in the times of Ahaz and Manasseh it became notorious as the scene of the barbarous rites of that deity and of Chemosh, when the idolatrous inhabitants of Jerusalem cast their sons and daughters into the red-hot arms of a monster idol of brass placed at the opening of the ravine (2 Kings 16:3; 2 Chronicles 28:3; Jeremiah 7:31). To put an end to these abominations the place was polluted by Josiah, who spread over it human bones and other corruptions (2 Kings 23:10; 2 Kings 23:13-14), from which time it seems to have become the common cesspool of the city. These inhuman rites and subsequent ceremonial defilement caused the later Jews to regard it with horror and detestation, and they applied the name given to the valley to the place of torment.

the same is Jerusalem As Bethel was in earlier times called Luz(Genesis 28:19), and Bethlehem was called Ephrath(Genesis 35:16; Micah 5:2), so Jerusalem was called Jebus(Judges 19:11; 1 Chronicles 11:4). It is interpreted by some to mean a place "dry" or "down-trodden like a threshingfloor," which is thought to prove it must have been the south-western hill.

went up to the top of the mountain From the ravine of Hinnom the border now ascended to the top of the mountain that lieth before the valley of Hinnom westward, which is at the end of "the Valley of Giants northward." The "Valley of the Giants" was "the Valley of Rephaim," an ancient settlement of this giant tribe, from which sprang Og king of Basan, possibly after they were driven from their original seats by Chedorlaomer (Genesis 14:5). It was a "valley-plain," extending in a S.W. direction from Jerusalem to Mar Elias, spacious enough to serve as a camp for an army. Here (a) David twice encountered the Philistines and inflicted a destruction upon them so signal that it gave the place a new name, Baal-perazim = "the plain of Bursts" or "Destructions" (2 Samuel 5:17-20). Here (b) too it was in all probability that the incident of the water of Bethlehem occurred (2 Samuel 23:13).

the mountain here alluded to was the slight "rock-ridge" which on the north constitutes the boundary of the valley of Hinnom.