Joshua 13:16

And their coast was from Aroer that [is] on the bank of the
river Arnon
As the country of Sihon is described, ( Joshua 13:9 ) ; from whence it appears that it was his country which was given to Reuben, though not all of it:

and the city that [is] in the midst of the river;
(See Gill on Joshua 13:9);

and all the plain by Medeba;
which reached unto Dibon, ( Joshua 13:9 ) .