Three months after the great Macedonian victory in Gaugamela, Alexander marches his army into the Achaemenid heartland. Invading Persia requires a forceful approach via the mountains. To impede Alexander’s progress, one of Darius’ faithful satraps was put in command, while the King of Kings collected a fresh army to meet the invaders. 

It’s late October in 331 BC. It is not long before word of Darius’ terrible loss near Gaugamela reaches his wide dominion. As the victorious Macedonian army approached the affluent towns of Babylon and Susa, Persian satraps debated whether to stay loyal to the Achaemenids or bow to Alexander. The satraps of Mesopotamia, hearing how the Macedonian conqueror dealt with the previous Persian governing elite, chose to swap sides and relinquish their provinces to maintain local authority and positions. Alexander amassed vast treasures by conquering these towns, which he divided with his troops to reward their valour and devotion.

However, a large sum was sent back to Greece to help Antipater, the Hellenic League’s hegemon in Alexander’s absence, in his battle against the renegade Spartans. Both cities acquiesced to the new Macedonian control. Even Mazaeus, who commanded the Persian right wing at Gaugamela, remained governor of Babylon. Alexander sent Greek garrisons to secure new subordinates’ allegiance and shortly left for the Achaemenid heartland. However, Alexander was concerned that certain eastern satraps may still be loyal to Darius, who was said to be gathering another army to confront the invaders. With the massive Zagros Mountains guarding the entrance to Persia, Alexander chose to split his army into two halves, thereby dividing the danger. The larger, slower component was dispatched south, around the mountains, under Parmenion’s command. Alexander led the small, agile troop directly to Persia, via the treacherous Zagros Mountains. Soon his armies reached the Uxians, a mountain tribe who refused to submit to Persian dominion and demanded tribute from every Persian army passing through. However, Alexander preferred making new rules than observing old ones.

A year later, he attacked their town, killed several of their men, and compelled the others to pay a tribute. After hearing of the recalcitrant tribe’s fate, no one dared trouble the Macedonians again. Days passed as Alexander marched his army eastward. The journey got so boring that the Macedonian monarch stopped sending scouts ahead. The Greek army did not halt when it reached the 2 km wide plain and went right through the Persian Gates. Suddenly, Macedonian troops saw individuals on the slopes. They assumed these folks were merely refugees and marched on. The road curved southeast, with the sun obscuring the view ahead. When the Macedonian vanguard approached the pass, the road took a sudden curve and soon met a formidable earth and rock wall. Alexander presumably realized he had made a terrible mistake, but it was too late to escape. Thousands of Persian warriors poured down the slopes, pelting the befuddled Macedonians.

Ariobarzanes, the Persian satrap, remained faithful to Darius and planned a surprise assault to disrupt Alexander’s preparations and give the Persian heartland time to prepare. Ambushed, the Macedonians rushed to defend, but many fell, and it became evident that they could either carve their way out to the plain or perish in the valley. Alexander ordered a general withdrawal to preserve his troops and reduce casualties, a difficult decision given that many Greeks were still fighting in the valley. They were quickly defeated by the overwhelming Persian troops, while the Macedonian army advanced into the plain. A Persian commander had never outwitted Alexander. Ariobarzanes had p

lanned and executed an ambush perfectly. Macedonians established up camp in the valley and cared for the injured. Alexander faced adversity. They were trapped in the mountains in the dead of winter, with many foes ahead. The Persian Gate was the only known army-friendly pass. Days passed while the Macedonian leadership considered breaking the Persian blockade. In the battle of Thermopylae, a local shepherd is claimed to have led Alexander across the mountains to the Persian rearguard. In any case, the Macedonians ultimately broke the Persian defense, and with supplies running low, they arranged a fresh onslaught.

Night fell. Alexander led his forces northeast through the passes, while Craterus’ army lighted several campfires to draw the Persians’ attention to the camp. Craterus marched his surviving forces to the valley, feigning an assault. The sound of Macedonian horns rang in the valley in the Persian rear, and Alexander’s detachment unexpectedly emerged from behind and assaulted the unaware camp defenders, while another force under Philotas attacked the Persians atop the hill. The Persians were forced to fight in unsuitable situations, and they were no match for the ferocious and battle-hardened Macedonians, who swiftly outclassed Ariobarzanes’ army. His battalion was encircled and murdered as he refused to surrender and fought to the death. Contrary to popular belief, Ariobarzanes’s fight was the last stand of organized Persian defense. On the horizon stood Persepolis, the Achaemenid Empire’s ceremonial capital.