Alexander the Great vs Darius III: The Battle for Persia

When King Philip II of Macedonia was assassinated in 336 BC, the crown and the army he had built passed to his son. Alexander was just 20 years old. Despite his youth, he would lead his armies into battle time and again, never once tasting defeat. Through superior planning, tactical instinct, and intelligence, he became one of the most successful military commanders in history, finishing his career with an undefeated record.

His conquests stretched across nearly 12 years, but one of his most stunning victories was also one of his earliest: the destruction of the Achaemenid Empire, the First Persian Empire. Ruled by Darius III, Persia was the largest empire the world had ever seen up to that point, a power that had dominated western Asia for more than two centuries. It fell to Alexander in a series of decisive battles, fought principally at Granicus, Issus, and Gaugamela.

The full conquest was long and tangled, a campaign of sieges, marches, and political maneuvering across thousands of miles. But the empire’s fate was sealed in those three field battles, where a smaller, better-drilled army repeatedly broke a much larger one. This is the story of how Macedonia brought down a colossus, and of the duel between two kings whose contrasting fortunes decided the future of the ancient world.

Why Persia Was the Target

To understand why Persia was Alexander’s first objective, and how Macedonia could even hope to match such a vast empire, the story must begin before Alexander was born. From roughly 499 BC to 450 BC, a series of conflicts collectively known as the Greco-Persian Wars saw the Persian Empire launch repeated attacks in an effort to conquer Greece.

Greece at this point was not a single country but a region of several independent city-states. Ultimately those city-states, led chiefly by Athens and Sparta, formed an alliance and managed to defend against the invading Persian forces, securing peace in the region. The memory of those invasions lingered for generations, and it gave any future campaign against Persia a powerful moral framing: this would be a war of revenge for wrongs done to their forefathers.

A century later, those same city-states were again at war, but not with the Persians. They were fighting each other. The political landscape that Alexander would inherit was one of Greek division, and it was Macedonia that had risen to exploit it.

Philip II and the League of Corinth

Under the rule of Alexander’s father, King Philip II, Macedonia had become the dominant kingdom in the area, with the largest army, the most resources, and the most land. Many of the other city-states, mainly Athens and Thebes, saw Philip’s power as a looming threat to their own independence. They declared war on Macedonia and on whatever city-states would side with them.

The confrontation culminated at the Battle of Chaeronea, where, in a single engagement, Macedonia and its allies defeated Athens and Thebes in what many historians describe as the most decisive victory in history. The armies of Athens and Thebes were annihilated and could no longer wage war against Philip’s Macedonia.

As a result, every Greek city-state except Sparta entered an alliance known as the League of Corinth, or the Hellenic League. This new coalition voted Philip, distinctive with his missing eye, as the military leader for an upcoming campaign against the Persian Empire, a war that would avenge their forefathers, liberate allied city-states still under Persian occupation, and ensure that Persia would never again be a threat.

But before those plans came to fruition, Philip was suddenly assassinated in 336 BC. The throne and the command of the invasion passed to his son. Alexander was now king of Macedonia and the appointed general of an alliance preparing to march against the mightiest empire of its age.

A Vulnerable Empire

Persia, normally seen as a symbol of stability and prosperity, was in a fragile state at the moment Alexander prepared to strike. The Persian king Artaxerxes III had been recently murdered, leaving the throne to Darius III. Egypt had revolted against Persian occupation. And the Persian fleet was not nearby to respond. If there was ever a window for Alexander to launch his invasion, this was it.

The first encounter between Alexander’s army and the Persians came at the river Granicus in May, 334 BC. Today that river is called the Biga River, in northwestern Turkey. Alexander approached from the west, but the Persians were waiting on the eastern bank, which meant the Greeks would have to cross the river and its muddy banks under fire in order to fight.

Estimates of the armies’ sizes vary wildly, from as few as 20,000 to over 600,000 men. The general consensus is that both sides fielded somewhere between 30,000 and 40,000, a figure that lines up with the numbers in the battles that followed, though it remains an estimate. What is known for certain is that Persia had several thousand more heavy cavalry than Macedonia, and had also hired Greek mercenaries, men intimately familiar with Macedonian tactics.

The Battle of Granicus

The Persian cavalry was placed at the front of the army, waiting to charge any infantry that attempted to cross the river, with archers and light infantry stationed behind them, a formidable sight to the approaching Macedonians. Despite having marched all day to reach the river, Alexander decided that camping for the night was not his style and ordered an immediate crossing of the Granicus to attack.

King Darius III was not present at this fight, likely because he underestimated the threat the Macedonian army posed. Instead he sent his satraps, or nobles, to deal with it, alongside a Greek mercenary named Memnon of Rhodes. But Alexander, in his flashiest armor and decorated helmet, would never pass up a chance to lead his army headfirst into battle. The Greek cavalry split into two groups on the flanks, with Alexander leading the right and his right-hand man, Parmenion, leading the left.

The battle began as the Macedonian heavy infantry, in phalanx formation, started crossing the river in the center, immediately becoming a target for the Persian archers on the far bank. As thousands of arrows and thrown spears struck the phalanx, the cavalry on either end charged across the river. Parmenion and his horsemen crossed and moved straight ahead, engaging the Persian cavalry positioned to intercept them. Alexander, by contrast, ignored the cavalry directly in front of him and drove his own force straight into the Persian center, scattering the archers and giving his infantry the chance to complete their crossing.

Alexander in the Thick of It

As the Persian cavalry realized what was happening, they wheeled around Alexander’s force, producing some of the most intense fighting of the entire battle. Despite being nearly surrounded on the Persian half of the river, Alexander’s cavalry held firm. The Macedonian horsemen were expert wielders of the xyston, a long, fearsome spear that often had two pointed ends, giving them an advantage against the shorter Persian javelins.

Alexander himself fought fiercely. When his spear snapped in half, without missing a beat he took another from one of his generals and continued his attack. He then spotted Mithridates, a Persian noble and cavalry leader. Alexander charged him, and after a brief clash emerged victorious by thrusting his spear into Mithridates’ face.

But the bold charge had left Alexander exposed. Another Persian noble, Rhoesaces, charged him from behind and struck his helmet with his sword. Alexander’s helmet was punctured and his head was bleeding, but he turned and killed Rhoesaces nonetheless. As a third noble, Spithridates, swung his sword at Alexander, the attacker’s arm was severed by one of Alexander’s bodyguards, Cleitus the Black.

The Persian center had been broken, and the Macedonian infantry was now arriving steadily from the Granicus, marching forward in tight phalanxes. The Persian armies began to flee. Alexander’s men did not chase them far, focusing instead on the Greek mercenaries who had been fighting for the enemy. Parmenion’s cavalry circled behind those mercenaries, leading to their absolute defeat, with thousands killed and thousands more taken prisoner.

The Aftermath of Granicus

In the end, Granicus was a massive victory for Alexander. Most sources say as few as 150 Greek soldiers were killed, with about a thousand wounded. On the Persian side, it is possible that up to 2,000 cavalrymen were lost, along with 3,000 of their mercenaries killed and another 2,000 taken prisoner.

The battle also showed Alexander’s men that they could rely on him in combat. He had, after all, taken a sword to the head, and some sources even say he fell unconscious during a portion of the fight as a result. But crucially, once the battle was won, the Macedonians looted the abandoned Persian camps, sending much of the spoils home and providing much-needed financial support to the campaign.

After the defeat at Granicus, King Darius III realized he had underestimated the Macedonian army, and that it was now a genuine threat to his entire empire. To put an end to the invasion, Darius began amassing an army to confront Alexander himself.

The Road to Issus

With the initial Persian resistance out of the way, Alexander’s army moved essentially uncontested through western Asia Minor, liberating cities that welcomed him and besieging those that resisted. Another important Macedonian objective was to capture as many Persian port cities as possible. This way the Persian fleet, far too large for the Macedonian navy to challenge directly, would be unable to land reinforcements to support Darius.

After capturing important coastal cities such as Ephesus, Halicarnassus, and Miletus, the Persian navy had nowhere to safely land reinforcements behind the Macedonians. To ensure this, Parmenion was sent with a large force to occupy the area around the town of Issus. It was also during this period that Alexander captured the city of Gordion, home to a knot so large and complex that local legend held the man who could untie it was destined to rule Asia. After inspecting the knot, Alexander drew his sword and sliced it open.

As he continued through Asia Minor, Alexander was aware that Darius was to the east, in Babylon, assembling an army. But in the autumn of 333 BC, his scouts informed him that King Darius was marching closer. Alexander gathered his forces and marched south of the town of Issus, into a narrow mountain pass where he rejoined forces with General Parmenion. His hope was that Darius would take the quickest route to him, leading the Persians south through the Belen Pass, to the west of which the Macedonians would be waiting to ambush them.

The Battle of Issus

Darius, possibly anticipating this, moved his army to the north, taking the longer route around the Amanus Mountains, today known as the Nur Mountains, in south-central Turkey. This allowed Darius to swing wide behind Alexander’s army, and he captured the now defenseless city of Issus, where the Macedonian sick and battle-wounded were resting. Darius had them all killed and began marching southbound, behind Alexander, cutting off the Macedonian supply lines.

This forced Alexander’s hand, and he immediately marched northward for battle. The two armies caught sight of each other on November 5, 333 BC, south of the town of Issus at a small river known as the Pinarus.

This time, Darius had used his empire’s vast resources to amass an army much larger than Alexander’s. Most sources say the Macedonian army was about 40,000 men, while the Persian army was likely more than double that size. The Persians again brought hired Greek mercenaries, cavalry, and all 10,000 Persian Immortals, an elite heavy infantry unit.

Darius wanted to fight Alexander in an open field where the advantage of his immense numbers would be felt, but the Gulf of Issus, where the battle was about to take place, was only a couple of kilometers wide between the sea and the mountains, meaning he could not take full advantage of the size of his army. Darius was also surprised to find the full force of Macedonia there, as he was unaware Alexander had beaten him to Parmenion, having hoped to face each of their forces individually while they were still separated.

Breaking the Persian Line at Issus

Alexander stationed his troops just as he had at Granicus: cavalry on the left, led by Parmenion; phalanx in the center; and Alexander with his elite companion cavalry on the right. This time, though, Darius threw the first punch. His cavalry, positioned near the beaches on Alexander’s left, charged across the small river, hoping to overwhelm Parmenion’s horsemen. In response, the Macedonian phalanx began its attempt to cross the river, its formation once again relentlessly struck by thousands of Persian archers.

Initially, the tide was shifting in favor of Persia. Parmenion’s cavalry on the left was heavily outnumbered, and the center phalanx was slowly coming undone under the sheer number of enemies pushing it. But Alexander and his companion cavalry managed to charge across the river on the right, near the mountains, and crushed the infantry that resisted them, breaking a hole in the Persian defensive line. He then made a quick decision to flank behind the enemy lines to aid his phalanx.

Now under attack from three sides, the Persian center quickly began to crumble. The Macedonian phalanx moved like a machine through the enemy lines, their long spears making quick work of anyone who got too close. Darius realized the danger he was in and turned around and ran. Alexander and many of his troops stormed after him but were unable to catch the king himself.

The Persian cavalry, despite its initial success against Parmenion, also turned and fled, suffering heavy losses as they attempted to escape, saved only perhaps by the Macedonians stopping the chase as the sun fell below the horizon.

The Battle of Issus was another devastating loss for Persia. Darius had lost at least 20,000 soldiers, while under a thousand Macedonians were killed, with between five and seven thousand wounded. Alexander had shown that discipline and training could defeat sheer numbers. But Darius was still alive, already preparing for a rematch, and he would not make the same mistakes twice.

The Buildup to Gaugamela

For the next couple of years, Darius retreated to Babylon, deep in his empire, to decide how to handle the invasion, while Alexander continued his conquest of Persian territories. First he besieged Tyre, then successfully attacked Gaza. When he arrived in Egypt, he did not have to fight; its people were more than happy to be liberated from Persian occupation.

As Alexander snatched one city after another, Darius tried his luck with a more diplomatic approach, drafting three separate treaties presented to the Macedonians, each more generous than the last. All three were rejected, even though the final offer included letting Alexander co-rule the empire and offered one of Darius’s own daughters to be his wife. Desperate times, it seems, called for desperate measures.

As the Macedonian army moved eastward, Darius assumed Alexander would advance to the southeast, along the banks of the Euphrates to Babylon. To counter this, Darius employed a scorched-earth tactic, burning and plundering the land ahead of time, leaving no food or supplies for an invading army moving through the area. The strategy had been suggested to Darius years earlier, when Alexander first entered his kingdom, but Darius had ignored it until now.

Alexander, instead of heading southeast along the Euphrates as Darius expected, headed northward, opting to cross the Tigris river first, looting rural villages as he went rather than assaulting heavily defended cities. Darius sent an advance party, led by a noble named Mazaeus, to burn and plunder the eastern banks of the Tigris before Alexander crossed, but it failed to arrive in time to prevent the crossing. By the lunar eclipse on October 1st, 331 BC, both armies were on the eastern side of the Tigris. Darius looked for an optimal place to wait for Alexander and chose a wide, flat plain near the village of Gaugamela, not wishing to be caught in the same geographical trap he had been lured into two years prior.

The Armies at Gaugamela

Alexander was initially unaware of the Persian army’s location, but his soldiers managed to capture some of Darius’s scouts and learned the enemy was just to the east. Alexander immediately marched in their direction. As he approached, his army was spotted by a small Persian force on a hill next to the open fields. This smaller group, led by Mazaeus, understandably did not want to fight the entire Macedonian army, so they simply retreated back to the main camps, handing Alexander the high ground.

But Darius was confident in his positioning, as the open field below the hill was well suited to the number of soldiers he had with him. Most sources place the Persian army at over 100,000 men. Darius had once again brought his 10,000 Immortals, tens of thousands of infantry, plenty of cavalry, and this time even 15 Indian war elephants and several bladed chariots. The Macedonian force, by contrast, was about 47,000 strong.

From his vantage point on the hill, Alexander could see the entire Persian formation and every enemy movement. He knew Darius would not dare risk attacking his well-defended hill, so Alexander took his time, ensuring his soldiers were well-rested, fed, and prepared for war the next day. Conversely, Darius was under constant threat of a sudden Macedonian charge, and his soldiers had to be ready for battle at a moment’s notice, even throughout the night leading up to the fight, fatigue that would tell the following day.

The Trap at Gaugamela

As the sun crested the horizon the next morning, Alexander’s men marched down the hill and positioned themselves for combat. The Macedonian formation was once again a line with a phalanx center and cavalry on each side, but this time the wings curved backward slightly, to avoid being surrounded by an enemy flanking maneuver. Alexander once again took his companion cavalry on the right edge and trusted the left side to Parmenion.

As Alexander moved to attempt a wide charge on the right, the Persian cavalry charged his position, but the elite companion cavalry held their ground, pushing the Persians back. Darius then commanded his chariots to speed into the Macedonian phalanx. The Macedonians had trained for such a threat, and they responded by breaking formation and allowing the chariots to enter their lines, after which they quickly surrounded them, making quick work of the chariots with their three-meter pikes as they rode through.

With the chariots out of the fight rather quickly, Darius ordered his remaining cavalry to attack the Macedonian left flank, where Parmenion was stationed. Though heavily outnumbered, Parmenion’s cavalry were able to hold their line for quite some time.

With the entirety of the Macedonian cavalry occupied at both flanks, Darius seized an opportunity to strike the formation’s weak center. As his Immortals charged toward the Macedonian phalanxes, it seemed as if Darius had the upper hand, but this was a trap. Alexander had anticipated the move. When the front line of Persian infantry reached the Macedonian line, Alexander’s cavalry, triumphant on their right flank, immediately charged toward the Persian center, straight at Darius and his royal bodyguards, who were now left without their 10,000 Immortals.

The Fall of Persia

The second line of Persian infantry stepped up, but despite numbering in the thousands, these units were poorly trained and equipped, especially in contrast to Alexander’s elite cavalry. As Alexander slashed his way toward Darius, eager to take his crown, the Persian king ran away for the second time. Alexander started to chase him but quickly turned around and headed to aid Parmenion. The remaining Persian forces were swiftly surrounded and destroyed.

Alexander lost around a thousand soldiers at Gaugamela, but it is estimated that Persia lost more than 40,000.

Alexander had humiliated Persia’s army for the third time in just three years. With this latest victory, he had gained control over the central regions of the empire, giving him the chance to attack Persepolis, the capital of the Persian Empire, which he successfully captured and burned. And while Alexander was disappointed that Darius had slipped through his fingers a second time, he would never face him in battle again.

Following the defeat, Darius once again attempted to amass an army, but struggled to gather a force of sufficient magnitude. This was partly due to his shrinking empire and the diminishing support of his own people, who were losing confidence in his ability to match Alexander tactically. In fact, Alexander was not even meeting much resistance from some occupied Persian cities, as, among other liberal policies, he allowed them to continue practicing their own religion.

Darius was eventually murdered by his relative, the noble Bessus. Bessus and the leader of the Persian palace guard bound Darius to an ox cart in the desert. As Alexander approached, they fled, wounding Darius and leaving him to die before the Macedonians reached him. Darius’s killers were caught and executed shortly thereafter.

Alexander was disappointed that he did not capture Darius alive, but he sent the body back to Persepolis, where it was given a grand funeral and buried in the royal Persian tombs. Alexander was now officially the King of the Persian Empire. And that daughter Darius had offered him earlier? He married her anyway.