Numbers 21:13

13 From there they marched and camped across the Arnon in the desert that extends from the border of the Amorites, for the Arnon was the border of Moab, between Moab and the Amorites.

Numbers 21:13 Meaning and Commentary

Numbers 21:13

From thence they removed, and pitched on the other side of
Arnon
A river on the borders of Moab:

which is in the wilderness that cometh out of the coasts of the
Amorites;
according to Jarchi, they went round the land of Moab, all to the south and east, and came not into the border of Moab, as Jephthah said, ( Judges 11:18 ) but before they came hither they had a station at Almondiblathaim, ( Numbers 33:46 Numbers 33:47 )

for Arnon is the border of Moab, between Moab and the Amorites;
a river which divided these two countries, and bounded them; and Moses is the more particular in this account, to show that the Israelites took nothing from the Moabites, but what the Amorites had taken from them, they being charged not to distress the Moabites and Ammonites, ( Deuteronomy 2:9 Deuteronomy 2:19 ) , see Jephthah's defence, ( Judges 11:15-27 ) .

Numbers 21:13 In-Context

11 They marched from Oboth and camped at Iye-abarim in the desert on the border of Moab toward the east.

12 From there they marched and camped in the Zered ravine.

13 From there they marched and camped across the Arnon in the desert that extends from the border of the Amorites, for the Arnon was the border of Moab, between Moab and the Amorites.

14 For this reason the scroll of the LORD's wars says: Waheb in Suphah and the ravines. The Arnon

15 and the ravines that extend to the settlement of Ar and lie along the border of Moab.