'Frontier' in the Bible

Then the Israelites heard it said, “Look, the Reubenites, Gadites, and half the tribe of Manasseh have built an altar on the frontier of the land of Canaan at the region of the Jordan, on the Israelite side.”

therefore I am about to expose Moab’s flank beginning with its frontier cities, the pride of the land: Beth-jeshimoth, Baal-meon, and Kiriathaim.