Arnon is a river valley east of the Dead Sea, and in the books of Moses it works as a border. Israel camps on its far side, “the border of Moab, between Moab and the Amorites” (Numbers 21:13). When Sihon, king of the Amorites, will not let Israel pass, the people cross the river and take his land. Later Moses recalls that Reuben and Gad received their territory from Gilead to this river. A very old song about the LORD’s wars even remembers “the brooks of Arnon.” Deuteronomy 2:24-37 tells how Israel crossed it.
8 verses
From thence they removed, and pitched on the other side of Arnon, which is in the wilderness that cometh out of the coasts of the Amorites: for Arnon is the border of Moab, between Moab and the Amorites.
Wherefore it is said in the book of the wars of the LORD, What he did in the Red sea, and in the brooks of Arnon,
For Heshbon was the city of Sihon the king of the Amorites, who had fought against the former king of Moab, and taken all his land out of his hand, even unto Arnon.
And when Balak heard that Balaam was come, he went out to meet him unto a city of Moab, which is in the border of Arnon, which is in the utmost coast.
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.
From Aroer, which is by the brink of the river of Arnon, and from the city that is by the river, even unto Gilead, there was not one city too strong for us: the LORD our God delivered all unto us:
And we took at that time out of the hand of the two kings of the Amorites the land that was on this side Jordan, from the river of Arnon unto mount Hermon;
And unto the Reubenites and unto the Gadites I gave from Gilead even unto the river Arnon half the valley, and the border even unto the river Jabbok, which is the border of the children of Ammon;
Matthew George Easton, 1897
Swift, the southern boundary of the territory of Israel beyond Jordan, separating it from the land of Moab (Deut. 3:8, 16). This river (referred to twenty-four times in the Bible) rises in the mountains of Gilead, and after a circuitous course of about 80 miles through a deep ravine it falls into the Dead Sea nearly opposite Engedi. The stream is almost dry in summer. It is now called el-Mujeb. The territory of the Amorites extended from the Arnon to the Jabbok.
William Smith, 1884
(roaring), the river or torrent which formed the boundary between Moab and the Amorites, on the north of Moab, (Numbers 21:13,14,24,26; Judges 11:22) and afterwards between Moab and Israel (Reuben). (2:24,36; 3:8,12,16; 4:48; Joshua 12:1,2; 13:9,16; Judges 11:13,26) There can be no doubt that the Wady el-Mojeb of the present day is the Arnon. Its principal source is near Katrane , on the Haj route.