48 This land extended from Aroer on the rim of the Arnon Gorge to Mount Siriona (that is, Hermon),

Read Deuteronomy 4:48 Using Other Translations

From Aroer, which is by the bank of the river Arnon, even unto mount Sion, which is Hermon,
from Aroer, which is on the edge of the Valley of the Arnon, as far as Mount Sirion (that is, Hermon),
So Israel conquered the entire area from Aroer at the edge of the Arnon Gorge all the way to Mount Sirion, also called Mount Hermon.