Heshbon was the city of Sihon king of the Amorites, who had fought against the former king of Moab and had taken from him all his land as far as the Arnon.
References for Numbers 21:26
That is why the poets say: “Come to Heshbon and let it be rebuilt; let Sihon’s city be restored.
“Fire went out from Heshbon, a blaze from the city of Sihon. It consumed Ar of Moab, the citizens of Arnon’s heights.
References for Numbers 21:28
Woe to you, Moab! You are destroyed, people of Chemosh! He has given up his sons as fugitives and his daughters as captives to Sihon king of the Amorites.
References for Numbers 21:29