After invading Achaemenid Persia in 330 BC, Alexander the Great sent the main force of his army to Persepolis by the Royal Road. He stormed the Persian Gates, a pass through modern-day Zagros Mountains. There Ariobarzanes of Persis successfully ambushed Alexander the Great's army, inflicting heavy casualties. After being held off for 30 days, Alexander the Great outflanked and destroyed the defenders. Ariobarzanes himself was killed either during the battle or during the retreat to Persepolis. Some sources indicate that the Persians were betrayed by a captured tribal chief who showed the Macedonians an alternate path that allowed them to outflank Ariobarzanes in a reversal of Thermopylae. After several months, Alexander allowed his troops to loot Persepolis.