Joshua 13:8, 16-17

With the other half-tribe the Reubenites and the Gadites received their inheritance, which Moses had given them, beyond the Jordan eastward, as Moses the servant of the LORD had given them

Their territory was from Aroer, which is on the bank of the River Arnon, and the city that is in the midst of the ravine, and all the plain by Medeba; Heshbon and all its cities that are in the plain: Dibon, Bamoth Baal, Beth Baal Meon