"The Myth of the Burning Garbage Dump of Gehenna
I have long wanted to do a little work to debunk the endlessly repeated myth that the Hinnom Valley (Gehenna) was a perpetually burning trash dump. There simply is no evidence to support the idea, but because it seems a reasonable explanation for the origin of the Hinnom Valley as “hell,” writers and preachers accept and propagate the story.
As with the legend about the rope around the high priest’s ankle, this popular myth seems to have originated in Jewish circles in the Middle Ages. McBride has more details and the sources in his post.
The explanation for the “fire of Gehenna” lies not in a burning trash dump, but in the burning of sacrificed children. Jeremiah is explicit that such occurred here:
Jeremiah 7:31–32 (ESV) — And they have built the high places of Topheth, which is in the Valley of the Son of Hinnom, to burn their sons and their daughters in the fire, which I did not command, nor did it come into my mind. Therefore, behold, the days are coming, declares the Lord, when it will no more be called Topheth, or the Valley of the Son of Hinnom, but the Valley of Slaughter; for they will bury in Topheth, because there is no room elsewhere.
Isaiah had already envisioned Topheth as the fiery destiny of an enemy of God.
It is not difficult to see, from these and other texts (e.g., 2 Kgs 23:10; 2 Chr 28:3, 33:6; Jer 32:35), why Jesus and his contemporaries used the word Gehenna (“valley of Hinnom”) as synonymous with the place of everlasting fiery torment. Indeed, there is no reason to search further for ancient burning piles of discarded newspapers, product packaging, and junk mail.
UPDATE (4/29): The views of various scholars on the matter is presented in a new post"
source