Commentary for Joshua 18:15

And the southern side— Referring to the southern border of Binyomin which is identical with the northern border of Yehudah. All the borders that are listed here are listed relative to the north of Yehudah, and every place described here as descending, is described in reference to Yehudah as going up because here he is listing [boundaries] from west to east and there he lists them from east to west.

And the boundary extended to the sea— to a sea, but I do not know which sea it is.