Charles Ellicott Commentary Deuteronomy 2:36

"From Aroer, which is on the edge of the valley of the Arnon, and [from] the city that is in the valley, even unto Gilead, there was not a city too high for us; Jehovah our God delivered up all before us:" — Deuteronomy 2:36 (ASV)

Aroer. —According to Conder, “the ruin ‘Ar ‘Air, on the north bank of Wâdy Môjib.” (But he makes the Aroer of Numbers 32:34 a different place, and marks it as unknown. Why?)

The city that is by the river. —The description suggests Rabbath-ammon, but this cannot be referred to here.