For Heshbon was the city of Sihon the king of the Amorites, who had fought against the former king of Moab, and taken all his land out of his hand, even unto Arnon.
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George Leo Haydock
Arnon. Hence this territory, which formerly belonged to Moab, being taken in a just war, the Moabites could not lawfully retain it, as they attempted to do under Jephte, Judges xi. 13. (Grotius, Jur. iii. 6.)
Hesebon, or Esbus, was the capital, and lay over-against Jericho, twenty miles from the Jordan.