Numbers 21:13

21:13 From there they moved on and camped on the other side of the Arnon, in the wilderness that extends from the regions ¹  of the Amorites, for Arnon is the border of Moab, between Moab and the Amorites.

Numbers 22:36

Balaam Meets Balak

22:36 When Balak heard that Balaam was coming, he went out to meet him at a city of Moab which was on the border of the Arnon at the boundary of his territory.

[21:13]  ¹ tn Or “border.”