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.

So the Moabites said to the elders of Midian, “This horde will devour everything around us like an ox eats up the green plants in the field.”

Since Balak son of Zippor was Moab’s king at that time,

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.