Joshua 13:23

And the border of the children of Reuben was Jordan, and the
border [thereof]
As their border eastward was Aroer on the river Arnon, so their border westward was the river Jordan:

this [was] the inheritance of the children of Reuben, after their
families, the cities and the villages thereof;
which Moses gave them on the other side Jordan; and next follow an account of the inheritance of the tribe of Gad in those parts.