Deuteronomy 2:24

“ Rise yourselves up, take your journey, and pass over the valley of the Arnon. See, I have given into your hand Sihon the Amorite, king of Heshbon, and his land. Begin to take possession of it, and contend with him in battle.”

They were now therefore to rise and cross the River Arnon and its valley and approach the Amorites, under Sihon king of Heshbon, north of Moab. In spite of the fact that Israel would offer friendship the result would be fierce battle during which they would commence taking possession of the land which was to be theirs. This was Yahweh's decision and His purpose. This land had been snatched from Moab by Sihon. It was not his, and he and his people were Amorites, due for destruction.

Heshbon was the royal city of the Amorites in the area (Numbers 21:25). It has not yet been clearly identified. It became a levitical city (Joshua 21:39). It was restored by Reuben (Numbers 32:37), came into the possession of Gad, and then was later in the times of Isaiah and Jeremiah taken by Moab, before again being captured by Israel