'Frontier' in the Bible

When the Israelis heard about it, they announced, "Look here, the descendants of Reuben, the descendants of Gad, and the half-tribe of Manasseh have constructed an altar in Canaan's frontier district of the Jordan River, on the side apportioned to the Israelis."

You gave them kingdoms and nations, apportioning them as frontier boundaries. They took possession of the land of Sihon, the land of the king of Heshbon, and the land of Og, king of Bashan.

therefore you'd better watch out! I'm going to tear open Moab's flanks, starting with its frontier cities the very glory of the nation! including Beth-jeshimoth, Baal-meon, and Kiriathaim.