Deuteronomy 2:24

Rise ye up, take your journey, and pass over the river Arnon: behold, I have given into thine hand Sihon the Amorite, king of Heshbon, and his land: begin to possess it, and contend with him in battle.

Rise ye up ... and pass over the river Arnon. At its mouth, this stream is 82 feet wide, and 4 feet deep: It flows in a channel banked by perpendicular cliffs of sandstone. At the date of the Israelite migration to the east of the Jordan, the whole of the fine country lying between the Arnon and the Jabbok, including the mountainous tract of Gilead, had been seized by the Amorites, who being one of the nations doomed to destruction (see Numbers 21:21; also Deuteronomy 7:2; Deuteronomy 20:16: cf. Hengstenberg, 'Pentateuch,' vol. 2:, pp. 347, 348; Kurtz, sec. 451, on the supposed inconsistency between this verse and Deuteronomy 2:24), were utterly exterminated, and their country fell by right of conquest into the hands of the Israelites. Moses, however, considering this doom as referring solely to the Amorite possessions west of Jordan, sent a peaceful message to Sihon, requesting permission to go through his territories, which lay on the east of that river. It is always customary to send messengers ahead to prepare the way.