John Wesley on Numbers 21:28

A fire - The fury of war, which is fitly compared to fire. Out of Heshbon - That city which before was a refuge and defence to all the country, now is turned into a great annoyance. It hath consumed Ar - This may be understood not of the city Ar, but of the people or the country subject or belonging to that great and royal city. The lords of the high places - The princes or governors of the strong holds, which were frequently in high places, especially in that mountainous country, and which were in divers parts all along the river Arnon. So the Amorites triumphed over the vanquished Moabites. But the triumphing of the wicked is short!