The territory of Reuben was an area of land east of the Jordan River. This land was given to the tribe of Reuben with the condition that they would help the other Israelite tribes capture the land of Canaan west of the Jordan River (Numbers 32). Moses agreed to the request from the Reubenites who wanted this land because it was good for raising cattle.
The Arnon River marked the southern border of the territory of Reuben. The stream of Heshbon and the kingdom of Ammon marked the northern and eastern borders. The Jordan River and the Dead Sea marked the western border.
The people of Reuben lived in this territory until around 732 BC, when they were taken into captivity (forced to leave their homeland) by Tiglath-pileser III, who was the king of Assyria.