Complex sentence: Etna made the path north of Naxos impassable, so Himilco had to risk dividing his forces, while the army under Himilco marched to detour around Mt.
Split into simpler sentences: Etna made the path north of Naxos impassable, so Himilco had to risk dividing his forces. While the army under Himilco marched to detour around Mt.