Joshua 13:8, 16-17

With the other half-tribe [of Manasseh], the Reubenites and the Gadites received their inheritance which Moses gave them beyond the Jordan eastward, just as Moses the servant of the LORD gave to them

Their territory was from Aroer, which is on the edge of the valley of the [river] Arnon, and the city which is in the middle of the valley and all the plain by Medeba; with Heshbon, and all its cities which are on the plain: Dibon and Bamoth-baal and Beth-baal-meon