They set out from there and camped on the other side of the Arnon River, in the wilderness that extends from the Amorite border, because the Arnon was the Moabite border between Moab and the Amorites.

Therefore it is stated in the Book of the Lord’s Wars:

Waheb in Suphah
and the ravines of the Arnon,

Israel struck him with the sword and took possession of his land from the Arnon to the Jabbok, but only up to the Ammonite border, because it was fortified.

Heshbon was the city of Sihon king of the Amorites, who had fought against the former king of Moab and had taken control of all his land as far as the Arnon.

For fire came out of Heshbon,
a flame from the city of Sihon.
It consumed Ar of Moab,
the lords of Arnon’s heights.

When Balak heard that Balaam was coming, he went out to meet him at the Moabite city on the Arnon border at the edge of his territory.