The Possession of the Cities of Sihon (Numbers 21:25-26).
‘And Israel took all these cities. And Israel dwelt in all the cities of the Amorites, in Heshbon, and in all its towns.'
Having defeated Sihon Israel took his cities, including Heshbon the capital city, one by one until all were in their possession. And subsequently they set up residence there, and throughout the whole country.
‘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 to the Arnon.'
Then it is explained that in fact Heshbon was the royal city where Sihon dwelt, and that he and the Amorites had captured it from Moab, a description of these events then being provided in a celebration ode.