The border went up the Valley of the son of Hinnom to the south side of the Jebusite hill (which is Jerusalem) and the border went up to the top of the mountain that lies on the west side of the Valley of Hinnom, which is at the north end of the Valley of Rephaim. Bible

“the Valley of the son of Hinnom to the south side of the Jebusite hill (which is Jerusalem).” The “Valley of the son of Hinnom” is better known as Ge-hinnom, or Gehenna, sometimes poorly translated as “hell.” The Hebrew word “ge” means “valley,” and Hinnom was the man’s name who first owned or occupied it. When Hinnom died, his sons inherited the land and the valley became the Valley of the sons of Hinnom. [For more on the Valley of Hinnom, Gehenna, see commentary on Matt. 5:22].

“which is at the north end.” The Rephaim Valley angles north as it nears Jerusalem. From Jerusalem, it runs south and west toward the Mediterranean Sea, and as it nears the sea it runs westward. This description of the border of Judah fits very accurately with the geography around Jerusalem. The sites are quite close together, giving a very accurate and detailed description of the border of Judah. People doubt the Scriptural record when it comes to history, but no one doubts the Scripture when it comes to geography. But the people who so accurately described the geography would have also accurately described the history. Also, only someone who knew the geography intimately could have written with such accuracy.

Commentary for: Joshua 15:8