Numbers 21:11

21:11 Then they traveled on from Oboth and camped at Iye Abarim, in the wilderness that is before Moab, on the eastern side.

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 of the Amorites, for Arnon is the border of Moab, between Moab and the Amorites.