There is no need to repeat those very many things, which are related of this place in the Old Testament; they are historical. The mention of it in the New is only mystical and metaphorical, and is transferred to denote the place of the damned. Under the second Temple, when those things were vanished, which had set an eternal mark of infamy upon this place, to wit, idolatry, and the howlings of infants roasted to Moloch, -- yet so much of the filthiness, and of the abominable name remained, that even now it did as much bear to the life the representation of hell, as it had done before.
It was the common sink of the whole city; whither all filth, and all kind of nastiness, met. It was, probably, the common burying-place of the city (if so be, they did now bury within so small a distance from the city). "They shall bury in Tophet, until there be no more any place," Jeremiah 7:32. And there was there also a continual fire, whereby bones, and other filthy things, were consumed, lest they might offend or infect the city. "There was a tradition according to the school of Rabban Jochanan Ben Zaccai. There are two palm-trees in the valley of Ben-Hinnom, between which a smoke arises: and this is that we learn, 'The palms of the mountain are fit for iron.' And, 'This is the door of Gehenna.'"
Some of the Rabbins apply that of Isaiah hither, chapter 66, verse the last: "They shall go out, and see the dead carcases of the men, that rebel against me; for their worm shall not die, and their fire shall not be quenched." -- "Those Gentiles (saith Kimchi upon the place) who come to worship from month to month, and from sabbath to sabbath, shall go out without Jerusalem into the valley of Jehoshaphat, and shall see the carcases of Gog and Magog," &c. And a little after; "The just shall go out without Jerusalem into the valley of Hinnom, and shall see those that rebel," &c.
What is to be resolved concerning the 'valley of Jehoshaphat,' he himself doubts, and leaves undetermined: "For either Jehoshaphat (saith he) here erected some building, or did some work, or it is called 'the valley of Jehoshaphat' because of judgment." So also Jarchi [on Joel 3:2]; "Jehoshaphat means all one with the 'judgments of the Lord.'"