The Arnon Valley is a deep canyon formed by the Arnon River. It sometimes marked the border between Moab and Edom (see Numbers 21:13). The river starts deep in the Arabian Desert and flows into the Dead Sea along its eastern shore.
Sihon the Amorite controlled the area east of the Jordan River, north of the Arnon River, and south of the Ammonite territories (see Numbers 21:21–35). No ancient records mention him except the Bible. His capital, Heshbon, was probably about 24 kilometers (15 miles) southwest of Rabbath Ammon. It is usually considered to be the same place as the impressive ruins at Tell Hesban.