A part of the land west of the Jordan was assigned to some of the families descended from Joseph's older son Manasseh. Machir, the father of Gilead, was Manasseh's oldest son and a military hero, so Gilead and Bashan, east of the Jordan, were assigned to him.
“When we took possession of the land, I assigned to the tribes of Reuben and Gad the territory north of the town of Aroer near the Arnon River and part of the hill country of Gilead, along with its towns.