The formidable canyon, which, at the top, measures some 3 km (2 mi) in width and is nearly 520 m (1,700 ft) deep, was crossed by only a few passages (Isa 16:2) and hence became an obvious natural boundary. At the time of the Israelite conquest it separated the Amorites on the N from the Moabites on the S (Nu 21:13), but Jephthah’s message to the Ammonites shows that the side to the N had once been under Ammonite control and had been invaded by the Amorites prior to Israel’s arrival. (Jg 11:12-27) Israel, having skirted the territory of Moab, reached the Arnon, probably at its upper reaches. Attacked by Sihon, the Amorite king, Israel gained the victory and took possession of the land from the Arnon up to the Jabbok. (Nu 21:21-24; De 2:24-36; see JABBOK, TORRENT VALLEY OF.) This first conquest thereafter became the territory of the tribes of Reuben and Gad.​—De 3:16; Jos 12:1, 2; 13:8, 9, 15-28.