Numbers 21:28
For there is a fire gone out of Heshbon, a flame from the city of Sihon: it hath consumed Ar of Moab, and the lords of the high places of Arnon. For there is a fire gone out of Heshbon, a flame from the city of Sihon: it hath consumed Ar of Moab, and the lords of the high places of Arnon.
The fire and flame going out from Heshbon, the city of Sihon, pictures the force of Sihon's conquest, whose power from Heshbon had spread over Moabite territory and consumed Ar of Moab and the lords of the high places of Arnon. The verse belongs to the account of Israel's victories over Sihon and Og east of the Jordan, for Israel defeated Sihon and afterward Og as God directed. The two kings were slain, the Amorites were destroyed, and Israel took possession of their land.
After that victory Israel moved forward and camped in the plains of Moab on this side of the Jordan by Jericho. Those recent victories over Sihon and Og were widely known, for Balak king of Moab and all Moab learned what Israel had done to the Amorites and saw Israel as a powerful people covering the face of the earth opposite them, and Balaam also knew of them. Learning this, Balak and all Moab were exceedingly terrified and troubled.
That terror, together with the Lord holding back the swollen Jordan before Israel, melted the hearts of the Amorite and Canaanite kings with fear. Because of that terror, Balak sought Balaam to curse Israel and drive them out. Balaam knew how completely God had defeated Israel's enemies, and therefore knew that his curse could not harm Israel while they remained faithful to God.