וּגְב֣וּל יָ֔ם הַיָּ֥מָּה הַגָּד֖וֹל וּגְב֑וּל זֶ֠ה גְּב֧וּל בְּנֵֽי־יְהוּדָ֛ה סָבִ֖יב לְמִשְׁפְּחֹתָֽם׃
And as for the west border, the Great Sea was the border thereof. This is the border of the children of Judah round about according to their families.
Read midrashic interpretation of Joshua 15:12: and classical rabbinic exegesis.