Numbers 21:13

13 From there they went on and put up their tents on the other side of the Arnon, which is on the waste land at the edge of the land of the Amorites; for the Arnon is the line of division 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 And journeying on again from Oboth, they put up their tents in Iye-abarim, in the waste land before Moab looking east.

12 And moving on from there, they put up their tents in the valley of Zered.

13 From there they went on and put up their tents on the other side of the Arnon, which is on the waste land at the edge of the land of the Amorites; for the Arnon is the line of division between Moab and the Amorites:

14 As it says in the book of the Wars of the Lord, Vaheb in Suphah, and the valley of the Amon;

15 The slope of the valleys going down to the tents of Ar and touching the edge of Moab.