Aroer, one of the Amorite cities, on the right bank of the river Arnon (cf. Joshua 12:2; Joshua 13:16). On the Moabite Stone, King Mesha says, "I built Aroer;" but this can only mean that, after some temporary condition of decay or ruin, he rebuilt it.
On the borders of the northern side of the Wady Mojeb, there are heaps of ruins bearing the name of Ara'ir, which probably mark the site of this ancient town. There was another Aroer, belonging at a later period to the tribe of Gad, and opposite to Rabba, the chief city of the Ammonites (Joshua 13:25; 2 Samuel 24:5); and still another in the south of Judah (1 Samuel 30:28), probably in what is now known as the Wady A'rarah.
The city that is by the river; properly, in the river or wady; i.e. At, the capital of Moab, which was in the valley of the Arnon, and which is mentioned here as marking the exclusive limit of the country that was captured.
The word rendered "river" ( נַחַל) is used of the valley or ravine (Arabic, wady) through which a stream flows, as well as of the stream itself (cf. Genesis 26:19; Numbers 24:6, etc.). Ar is elsewhere called Ar of Moab (Isaiah 15:1).
Even unto Gilead, i.e. Mount Gilead, which rises to the north of the Jabbok (hod. Zerka).