Aroer - Aroer on the Arnon (Deuteronomy 2:36 note). Aroer itself stood on the very edge of the precipitous cliff of the valley; and in the valley beneath, possibly in an island in the stream, stood another city which is here alluded to.
River - Rather, “the valley” (margin). They passed from Aroer, northward to Gad, and so pitched at Jazer (see the marginal references), which is on the frontier of Gad and Reuben.