ar'-non ('arnon; Arnon): Is first mentioned in Nu 21:24 as the border between Moab and the Amorites. "The valleys of Arnon" in the next verse undoubtedly indicate the numerous wadies contributary to the main stream. It formed the southern boundary of the land assigned to Reuben (De 3:12). The city of Aroer stood on the northern edge of the valley (De 2:36; Jg 12:2, etc.). Arnon was claimed by the Ammonites as having marked the southern limit of their territory when Israel invaded the land (Jg 11:13). They, however, had already been driven out by the Amorites, and the region north of Arnon was held by Sihon. From the inscription of Mesha on the Moabite Stone we gather that Moab had established herself on the north of the Arnon before the time of Omri. Under Omri and Ahab she was confined to the south of the river. A rebellion under Mesha was put down by Jehoram son of Ahab (2Ki 3:1-27), and the expedition of Hazael against Israel reached the valley of the Arnon (2Ki 10:33). But according to Mesha he regained for Moab the lost land; and this agrees with Isa 15:1-9; 16:1-14, where cities north of Arnon are located in Moab, e.g. Heshbon.
The modern name of Arnon is Wady el-Mojib, which enters the Dead Sea from the East about 11 miles North of el-Lisan. Some 13 miles East of the Dead Sea two streams, Seil es-Sa`ideh from the South, and Wady Enkeileh from the East, unite their waters and flow westward in the bottom of an enormous trench. The waters of Wady Welch come in from the Northeast. A wide stretch of country thus drains into the valley by means of a great network of smaller wadies--the "valleys of Arnon." The "fords of the Arnon" (Isa 16:2) were doubtless crossed by Mesha's highway which he claims to have built in Arnon; and may be marked by the traces of the old Roman road and bridge immediately to the West of where, on the northern edge of the Wady, stands `Ara`ir, the ancient Aroer.