Read “on the south,” and connect the words with the verse preceding. They indicate the southern limit of the still unconquered territory in this neighborhood, as Joshua 13:3 gives the northern one.
Mearah - The “cave” (see the margin) has been referred to “Mugar Jczzin” (“cave of Jezzin”), between Tyre and Sidon, or to a district characterized by deep cave-like ravines near Sidon and Dan-Laish.