Pitched on the other side of Arnon. The Arnon was without doubt the stream or torrent now known as the Wady Mojeb, which breaks its way down to the Salt Sea through a precipitous ravine. It must have been in the upper part of its course, in the desert uplands, that the Israelites crossed it; and this both because the passage lower down is extremely difficult, and also because they were keeping well to the eastward of Moabitish territory up to this point.
It is not certain which side of the stream is intended by "the other side," because the force of these expressions depends as often upon the point of view of the writer as of the reader. It would appear from Deuteronomy 2:26 that Israel remained at this spot until the embassage to Sihon had returned.
That cometh out of the coasts of the Amorites, i.e; the Aruon, or perhaps one of its confluents which comes down from the northeast. For Arnon is the border of Moab. It was at that time the boundary (see on Deuteronomy 2:26).