Judges 11:26 (ESV)

26 While Israel lived in Heshbon and its villages, and in Aroer and its villages, and in all the cities that are on the banks of the Arnon, 300 years, why did you not deliver them within that time?

Aroer was far south of Heshbon, on the north bank of the Arnon River, sixteen miles (twenty-five kilometres) east of the Dead Sea. It gets a mention here because it was the most important city on the border shared with Moab.1