Numbers 21:24 - Matthew Poole's English Annotations on the Holy Bible

From Arnon; or which reached from Arnon, &c. such supplements being very usual; and so here is contained a description or limitation of Sihon's conquest and kingdom, that it extended only from Arnon unto the children of Ammon; and then the following words, for the border of the children of Ammon was strong, come in very fitly, not as a reason why the Israelites did not or could not conquer the Ammonites, for they were absolutely forbidden to meddle with them, Deuteronomy 3:8; but as a reason why Sihon could not enlarge his conquests and empire to the Ammonites, as he had done to the Moabites. Jabbok; a river by which the countries of Ammon and Moab were in part bounded and divided. Was strong; either by the advantage of the river, or by their strong holds in their frontiers.