From there they moved on and camped on the other side of the Arnon, in the wilderness that extends into the Amorite territory. Now the Arnon is the border between the Moabites and the Amorites.
Jewish Publication Society of America Version (JPS1917) - Numbers 21:13 >From thence they journeyed, and pitched on the other side of the Arnon, which is in the wilderness, that cometh out of the border of the Amorites. — For Arnon is the border of Moab, between Moab and the Amorites;