Rashi on Joshua
From Kadush-barnea to Gaza. This refers to the south side of Eretz Yisroel going from east to west, but he did not conquer the entire boundary, leaving unconquered the area from Gaza to the [Mediterranean] Sea. This is what is stated below, “This is the land that remained [unconquered], the Gazites and the Ashdodites”16Chapter 13:2,3