Arnon

swift, the southern boundary of the territory of Israel beyond Jordan, separating it from the land of Moab (Deut 3:8 ; 3:16). This river (referred to twenty-four times in the Bible) rises in the mountains of Gilead, and after a circuitous course of about 80 miles through a deep ravine it falls into the Dead Sea nearly opposite Engedi. The stream is almost dry in summer. It is now called el-Mujeb. The territory of the Amorites extended from the Arnon to the Jabbok.

EBD - Easton's Bible Dictionary