Sihon, according to the Old Testament, was an Amorite king, who refused to let the Israelites pass through his country. The Bible describes that as the Israelites in their Exodus came to the country east of the Jordan, near Heshbon, King Siḥon of the Amorites refused to let them pass through his country. The Israelites fought Amorites in a battle, gaining complete victory. His walled towns were captured and the complete Amorite country was taken by the Israelites, who killed the king and "all his people." (Numbers 21:21-30, Deuteronomy 2:24-37). This is the first of many wars of annihilation mentioned in the Bible launched by the Israelites against Canaanite peoples .

"But Israel put them to the sword and took possession of their land, from the Arnon to the Jabbok, as far as [Az] of the Ammonites." (Numbers 21:24)

Moses allocated the land of Sihon, the king of Heshbon, to the Tribe of Gad in the allocation of land to the Israelite tribes. (Joshua 13:24-28)

In a similar way the Israelites took the country of Og, and these two victories gave them possession of the complete country east of the Jordan, from the Arnon to the foot of the Hermon. These victories, among the earliest successful campaigns of the Israelites, quickly became legendary among them, and are referred to numerous times in the Bible as prototypical examples of God-given victory.

Numbers 21:35 So they smote him, and his sons, and all his people, until there was none left him remaining; and they possessed his land. (King James Version)

Numbers 21:35 So they struck him down, together with his sons and his whole army, leaving them no survivors (New International Version)