Charles Ellicott Commentary Deuteronomy 2:24

"Rise ye up, take your journey, and pass over the valley of the Arnon: behold, I have given into thy hand Sihon the Amorite, king of Heshbon, and his land; begin to possess it, and contend with him in battle." — Deuteronomy 2:24 (ASV)

Pass over ... Arnon. — The territory from Arnon northward to Jabbok had been taken from Moab by the Amorites, and was to be possessed by Israel. (See Numbers 21:24.)