Moabites: The Territory East of the Jordan River, Bounded on the North by the Arnon River
Source: Nav
Numbers 21:13
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.
Judges 11:18
Then Israel traveled through the wilderness and bypassed the lands of Edom and Moab. They came to the east side of the land of Moab and camped on the other side of the Arnon. But they did not enter the territory of Moab, since the Arnon was its border.