The first king whom Moses and the Israelites defeated was an Amorite, King Sihon of Heshbon. The southern border of his kingdom ran down the middle of the Arnon gorge, taking in the town of Aroer on the northern edge of the gorge. The River Jabbok separated Sihon's kingdom from the Ammonites on the east. Then the Jabbok turned west and became his northern border, so his kingdom included the southern half of the region of Gilead.