Arnon: Boundary Between Moabites and Amorites
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Numbers 21:13, 26
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. / Heshbon was the city of Sihon king of the Amorites, who had fought against the former king of Moab and taken all his land as far as the Arnon.
Numbers 22:36
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.
Deuteronomy 2:24, 36
“Arise, set out, and cross the Arnon Valley. See, I have delivered into your hand Sihon the Amorite, king of Heshbon, and his land. Begin to take possession of it and engage him in battle. / From Aroer on the rim of the Arnon Valley, along with the city in the valley, even as far as Gilead, not one city had walls too high for us. The LORD our God gave us all of them.
Deuteronomy 3:8, 16
At that time we took from the two kings of the Amorites the land across the Jordan, from the Arnon Valley as far as Mount Hermon— / and to the Reubenites and Gadites I gave the territory from Gilead to the Arnon Valley (the middle of the valley was the border) and up to the Jabbok River, the border of the Ammonites.
Joshua 12:1
Now these are the kings of the land whom the Israelites struck down and whose lands they took beyond the Jordan to the east, from the Arnon Valley to Mount Hermon, including all the Arabah eastward: