The Ancient Macedonian Conquest of Persia

Alexander Mosaic, House of the Faun, Pompeii / Wikimedia Commons

The conquest of Persia was not preordained and those living within its vast empire could never foresee its fall.


In the year 356 BC, the Persian Empire still stood strong and seemed as if it would last another hundred years. However, on the 20th of July a sign was sent that brought the men of Asia great fear. While Alexander of Macedon was being born, a fire was raging in the great temple of Diana at Ephesus. This boy’s life would forever be entwined with those of the Persian Empire’s.

The conquest of Persia was not preordained and those living within its vast empire could never foresee its fall, but on closer inspection there appears to be cracks in its facade. Repeated revolts drained its coffers and defeat to the Greeks finally contained their hunger for more land. A series of royal executions and infighting further weakened the empire at a time when it needed to recover.

If Persia was so weak then why could the Greeks not take advantage of it before? The Greeks had a strong identity of individualism. Each polis wished to have the right to self-rule, but that did not stop the formation of leagues. The imperialistic ideals of Athens and Sparta caused the Greek world to be split into two large competing alliances. Decades of fighting at a stalemate weakened the allies of both poleis’ and allowed for other states to rise: Thebes and Macedon. The Greeks would not be able to conquer an empire without someone to unify them first.

If the Greek people couldn’t do it, then it fell into the lap of their northern neighbors the Macedonians. A young Philip II spent his early life in Thebes learning how to fight from one of the most preeminent generals of the day, Epaminondas. His aptitude for military matters allowed him to restructure the Macedonian military and lead it to victory against all those Philip wished to subjugate. Wars in Illyria and Greece created a trained army with an experienced officer corps. With a big showdown between Persia and Macedon looking inevitable, Phillip is assassinated leaving his legacy uncertain.

Alexander, a young prince, inherited the throne and the world was looking at what he would do. He was not only able to defeat the Illyrian and Greek rebels, but also prepare his kingdom for the biggest conquest yet in history. From the banks of the Aegean to the door step of India, Alexander destroyed his opponents through superior tactics. The only thing that could stop his desire to conquer was his own soldiers refusal to keep following him.

A Society of Independent Poleis

Left is which city-state is a member and right is how much was paid / Columbia College, Creative Commons

Whoever is the prominent military power during a specific time period that dominates many types of warfare and the largest force is usually the nation.  Before the year 479 BC, this nation was Persia.  However, even with all its given strength, the nation was beaten twice by the Greeks.  Even though it was thought that the Greeks were outnumbered by more than two to one.  Why then did the Greeks not move to conquer the Persians? The main factors why Persia had not been conquered before Alexander the Great is because of the political instability caused by Athens becoming an empire, a sense of Greek independence after the Persian threat, and the Peloponnesian War.

After the Persians failed to conquer Greece a second time under the leadership of Xerxes in 479 BC, it seemed that another attempt would be made to do so.  However, this did not occur because the Persians did returned to the Greek world.  Fearing the Persians would return at some point, the Greeks needed someone to lead them following the Persian War.  Originally, the leader of the Greeks was Pausanias of Sparta (Thucydides. The Peloponnesian War 1.128.3).  However, he came off as a dictator while he spent time in Ionia and barely lasted a year.  Following this chain of events, Sparta’s old rival Athens stepped into the scene and offered to lead the Greeks. The Greeks began creating leagues which other city-states joined.  The two dominant city-states that emerged as leaders were Athens and Sparta (Thucydides. History of the Peloponnesian War).   Athens became the head of the Delian League, and became a large power in ancient Greece during this time. This is shown by Athens collecting tribute in the forms of cash or ships to build the Athenian navy (see image below).  For nearly a quarter century, the Delian League fought against Persia.  The League was led by Cimon, who won many great victories against the Persians.  With the Persians removed from this area, a sense of security had come about.  The greatest victory came at Erymedon (476/6) when the Persians were effectively destroyed on land and sea.  (Thucydides The History of The Peloponnesian War).  However, with the Persian threat effectively neutralized, suspicions started arising.  Many city-states such as Naxos tried to leave, but the Athenians prevented them from doing so.  With the Persian threat removed, there were no apparent reasons to stay in the League.  This caused turmoil for the Greeks because many city-states that had become unified under a threat wanted to return to their old ways of independence.  Due to Athens forcing many city-states to remain in their League caused the city-states to believe that Athens had become an empire.  This feeling created more distrust throughout Greece.

Although Athens had become an empire, there was disunity within that caused for tensions that would eventually build up to the Peloponnesian War.  After Cimon’s successful battles, he returned home to Athens.  Pericles and Ephialtes were against Sparta, while Cimon was for Sparta (Plutarch. Pericles 9.3-10.6).  This shows more political instability within Greek city-states.  A devastating blow came to Cimon after the earthquake in Sparta and the Spartans turned the aid of Athens away when they called out for help.  This is shown by when Cimon stated, “Let’s no to allow Greece to go lame, or their own city be deprived of its yoke-fellow” (Plutarch’s Cimon 16.8).  On the other hand, Ephialtes said, “Let Sparta’s pride be trampled underfoot” (Plutarch’s Cimon 16.8).  Following this embarrassing event, Athens allied with Argos.  This action enraged the Spartans and tensions began to run higher.  Eventually, Cimon’s power was reduced, and Ephialtes and Pericles became the dominant political figures (Plutarch. Pericles).  Also, after the earthquake Athens started having conflicts with its neighbors.  One such example would be when Corinth and Athens were competing in a trade rivalry.  All of these factors led to the inevitable outbreak of the Peloponnesian War which weakened the Greeks.  The amount of political instability that took place during this time period prevented the Greeks of any chance they might have at actually moving into conquer the Persian Empire.

Potrait of Pericles who became a prominent leader of Athens during the Peloponnesian War / Wikimedia Commons

The first Peloponnesian War took place between the years 460-445 BC (Thucydides. The History of the Peloponnesian War).  The cause for the war the great amount of political conflict from many city-states.  However, this war did not last and was supposedly “undeclared”.  However, after a peaceful period between Sparta and Athens, tensions began to escalate again.  The war began in 431 BC and lasted until about 404 BC (Thucydides. History of the Peloponnesian war).  The first event that triggered the conflict was Corcyra told Potidaeda to remove Corinth citizens and tear down its walls (Thucydides. The Peloponnesian War 1.24-1.66).  The city-state refused, and the two city-states were at war with each side trying to draw Athens and Sparta into the fight.  Another event was when Megara was punished by Athens who was a member of the Peloponnesian League.  Diodorus tells us, “While these events were taking place the Megarians were finding themselves in distress because of their war with the Athenians on the one hand and with their exiles on the other hand” (Diodorus. Library of History12.66.1).  The city-state of Megara was cut off economically by Athens.  Thus the members of the Peloponnesian League were calling for Sparta to take up arms against Athens.  The argument present was Athens had become too powerful and were not respecting the difference in the poleis.  Also, in addition the Thebans attacked Plataea, and war broke out on all fronts.  The Spartans had proclaimed that they were going to liberate all of Greece from any form of tyranny (Thucydides. The Peloponnesian War 2.8).  Hearing this call of freedom, many city-states rushed to join the Spartans in their crusade.  Eventually, the Spartans were able to win the war and neither side really made any gains after decades of fighting.  Following these events, Sparta became imperialistic and Thebes allied with Athens to resist them.  Overall, fighting continued which left Greece severely weakened.  This paved the way for the Macedonians to invade Greece and unite all the different city-states under one banner.

After decades of fighting at a stalemate weakened the allies of both poleis’ and allowed for Thebes and Macedon to rise to power. Since the Greeks could not unite themselves, conquering Persia did not seem feasible.  In addition, many after the threat of the Persians, many city-states wanted to return to their independent ways.  However, the formation of leagues prevented these events from occurring.  Since the Greek poleis were not able to unite under one banner, the conquest of Persia would not occur.  That is until, the Macedonians were able to unite Greece, and a strong military leader came to launch such a conquest.

The Professionalization of the Macedonian Military

The Macedonians of the early 4th century did not look like a people who would conquer the known world. Macedonia was always an ally of whatever state was the most inclined to help it. Following the Theban’s devastating victory against the Spartans, the Macedonian king allied with them and sent a group of young hostages, including the future King Philip II, to show good face. Philip spent his time in Thebes with both Pammenes and Epaminondas, two of the greatest Theban generals (Plut. Pelop. 26.4-5). Green says, “He learnt the importance of professional training in drill and tactics, of close cooperation between cavalry and infantry, of meticulous staff planning combined with speed in attack” (Green 1991 15-16). Philip learned how to lead an army in Thebes and now free from being a hostage he decided to recreate the Macedonian army into a force to be reckoned with.

“Syntagma phalangis” by Alessandro Gelsumini / Wikimedia Commons

He had at his disposal the Hetairoi a heavy cavalry arm that even back in Thucydides’ day were described as “good horsemen” and “where they charged, none was able to resist them” (Thuc. 2.10). The weakness in the Macedonian military lied not with the cavalry but with the Pezetairoi, the infantry. The infantry was made up of tribal levies, peasants, and shepherds much like the infantry of Persia itself. Philip reorganized the infantry into a highly trained phalanx which wielded the sarissa, a spear over double the length of those commonly used (Green 1991 18-19). Philip’s training was exhausting and he would make his men march three hundred stades, thirty four miles, in full arms frequently (Polyaenus Strat. 4.2.10). The nobles were not safe from his discipline either. He beat one for leaving rank to find water and executed one for taking his arms off against orders (Aelian VH. 14.49).

This new army was first pitted against the Illyrians. The Macedonian phalanx stood firm and Philip sent his cavalry around the side to flank the enemy. After the infantry bloodied itself, the cavalry wheeled around and smashed the Illyrians. The fleeing Illyrians were chased and cut down leaving seven thousand dead (Diod. 16.4). Green examines the battle and sees proof of Philip applying the lessons he learned under Epaminondas. The oblique echelon was Epaminondas’ specialty. The Macedonian formation caused the Illyrian wing to stretch and once there was a gap, the Hetairoi were able to charge into it driving a great wedge (Green 1991 23-25).

The victory against the Illyrians ushered in an age of Macedonian expansion. Philip led his army around the Greek world establishing his dominance. According to Demosthenes, “he seized Amphipolis, next Pydna, then Potidaea, after that Methone, lastly he invaded Thessaly” (Olynth 1.12-13). His victories started to attract foreigners and before long he had an officer corps containing mercenaries from every part of Greece until it numbered about eight hundred (Green. 1991. 39). Philip continuously trained his soldiers and tried to improve them. He forbade the use of wagons due to their slow pace, limited the number of servants that could accompany the army, and refused to allow any women to stay at camp (Engels. 1978. 12-13). Philip’s reforms created an army that could appear so quick his enemies wouldn’t even expect him. His fastest rate was 18.9 miles in a day with his entire army, but while traveling with smaller forces he could double that (Engels. 1978. 20-23).

Battle of Chaeronea, 338 BCE / Wikimedia Commons

Philip continued to wage warfare against his neighbors until an alliance was formed against him. The Athenians chose to ask their old enemies, Thebes, to join them in the war against Philip (Diod. 16.85.1). On a plain north of Chaeronea, the two sides met. The Greek force was made up of twelve thousand Boeotians, led by the Theban Sacred Band, ten thousand Athenian hoplites, and five thousand mercenaries, according to Green (Green 1991 73). The Athenians made up a large percentage of the force and took the whole left wing but they were “impetuous and inexperienced” (Polyaenus. Strat. 4.2.7). In contrast, The Macedonian front line was full of experienced soldiers and the right wing, facing the Athenians, was led by Philip and he had a trick in mind. While Philip would command the infantry he put his son, Alexander, in charge of the cavalry. Alexander was to wheel around the flank and hammer into the Greeks, similar to the battle-plan used against the Illyrians (Green 1991 74-75). Philip’s well-trained phalanx was able to maneuver in a way a citizen militia couldn’t. He engaged the Athenians and then, keeping formation, slowly retreated causing the Athenians to push forward. Once they lost the advantageous high ground he brought his troops forward and attacked them with all his might (Polyaenus. Strat.4.2.2). The Macedonians were now on the high ground and a fatal flaw appeared in the Greek line. A gap was now opened between the Thebans and the rest of the line (Green 1991 75). Alexander took advantage of the situation and charged. What followed was a bloody fight that didn’t end until a thousand Athenians lay dead and the Theban Sacred Band was annihilated (Diod. 16.86.3-6).

The Battle of Chaeronea proved that Philip’s professional military was too experienced and could easily outmaneuver a citizen militia. The oblique echelon formation could create gaps in untrained enemy lines and a cavalry charge in the flank could shatter all but the bravest men. His surroundings pacified, Philip cast his eyes towards Persia.

Unfortunately, Philip was assassinated before he could leave to fight for the riches of Asia. What he left behind for his son was a military that could take on anyone. Years of warfare had created a core group of soldiers that would fight to the ends of the earth and an officer corps that had fought in multiple different situations. In particular, Parmenion, was Philip’s greatest officer and someone Alexander would make use of. Philip began allowing him to operate on his own by conquering the Illyrians (Plut.Alexander. 3.8). Parmenion was even sent to create a secure area in the Asian Hellespont to allow for the military to resupply and continue its way down the coast when it crossed into Persian territory (Diod. 17.2.4). Officers like Parmenion were capable of acting competently without oversight and that allowed Alexander to quickly stomp out rebellion when he took the throne without having to delay the war against Persia. This experienced military proved itself against heavily armored opponents and it was prepared for the light archers and light cavalry that made up most of the Persian drafted forces.

The Conquest of the Persian Empire

Alexander the Great had three major battles against the Persian Empire, those three battles were the battle of Granicus, the battle of Issus, and lastly the battle of Gaugamela. These decisive victories forced the Persian troops to retreat and given more time for Alexander to advance further into Persian territory.

“Battle Granicus” by Frank Martini. Cartographer, Department of History, United States Military Academy – The Department of History, United States Military Academy / Wikimedia Commons

The Battle of Granicus was the first major battle between the two powers. It took place on the river banks of the river Granicus in 334 BC. The army of Alexander consisted of 40,000 men and it was augmented by some troops already located in Asia. There are inconsistencies on the Persian army, Arrian claims 20,000 cavalry and 20,000 Greek mercenaries but in fact there was 4,000 – 5,000 Greek mercenaries. The Persians made a mistake of locating their cavalry on the river banks causing the cavalry to be a stationary unit as their infantry was located behind them (Diodorus, Book XVII, 19). Alexander exploited the Persian mistake and decided to attack on the same day he arrived. He countered the cavalry by using the  Pezhetairoi  (six battalions that consisted of 9000 infantry) at the center, 3,000  hypaspists on the right, with cavalry on the right flank, this is where Alexander was located (Arr 1.16.45 – 50). On the left wing were the Thessalian cavalry and some allied forces. Alexander began his attack by attacking the Persian left flank and drawing the center and weakening it. Given the opening he sought, Alexander ordered a direct attack of his companion on the right flank, followed by his entire army. Once the Persian cavalry retreated, as Alexander’s forces proved too much for the Persians, leaving the Greek mercenaries open for an attack. The Greek mercenaries of the Persians surrendered but Alexander refused to negotiate and proceeded to slaughter them to make an example of traitors. Of the 5,000 Greek mercenaries, 2,000 were left and  were sent to hard labor camps in Macedonia.

After his victory in Granicus, Alexander proceeded in occupying Asia Minor. Alexander sought to capture coastal settlements to reduce the power of the Persian Navy, as it was vastly superior to Alexander’s navy. Alexander captured Issus and kept marching south as he heard, Darius III, king of the Persian Empire, was located at Sochi. Darius marched north and went after Issus and recapturing before following Alexander’s trail south. Darius march south was interrupted, near the Pinarus River which had narrow coastal plain, when scouts spotted Alexander’s army marching north (Arr 2.6.2).

“Battle issus decisive” by Frank Martini. Cartographer, Department of History, United States Military Academy – The Department of History, United States Military Academy / Wikimedia Commons

Darius set his troops as best he could with the limitations the rough terrain provided, on the flat terrain he placed his infantry and barbarians on both sides, and on the right flank he placed his cavalry. Alexander placed his  pezhetairoi, carrying 18 foot long sarissas (Markle 1977), on the center; the Thessalian cavalry on the left, and the companion cavalry and Alexander were on the right. The battle plan was similar to the battle of Granicus, where the center infantry held the Persian infantry with the support of the left flank Cavalry as Alexander’s right flank cavalry overpowered the Persian left flank composed of barbarians. Due to the rough terrain the Macedonian infantry could not keep with the right cavalry creating an opening for the Greek Persian mercenaries to deal heavy damage (Arr. 2.10.7). Once The Macedonian cavalry had broken through the Persian left flank it went to support the infantry, causing Darius to flee the battlefield, causing instability on the remaining troops and they fled from the battlefield as well. This event marked a large victory on the Macedonian side, as no one had defeated the mighty Persian army with the king present.

“Battle of Gaugamela, 331 BC – Opening movements” / Wikimedia Commons

The final clash between Alexander’s forces and Darius’ forces was at Gaugamela in the summer of 331 BC, but this time the Persian army was at its greatest, as they had an open flat battlefield, as they had leveled it and cleared it (Curt. 4.13.36– 7), and larger numbers (Arr. 3.13.5– 6; Diod. 17.58.2– 5 and Curt. 4.15.14– 17). Alexander’s formation was similar to the formation used at Issus. The Macedonian cavalry in both flanks were tilted inward in anticipation of the Persian flanking maneuver, leading the Persian cavalry away from the heavy infantry center. Darius focused on the Macedonian right flank by sending his front forces there and creating a thinning on his lines to the left of Darius. Alexander was quick to take advantage of the situation, taking the companion Cavalry directly towards the weak spot. The Macedonian pezhetairoi clashed with the Persian infantry, while Alexander cut through the weak spot. Instead of counterattacking, Darius’ forces rode towards the Macedonian camp( Cf. Burn 1973: 118) , who were then slaughtered by the reserve troops in the back of the army. Darius, once again had to flee the battlefield, as his center forces collapsed and prevented himself from being captured.

Alexander’s final battle opened the entirety of Persia to him. Persian morale was broken after three incredible defeats and Alexander took no time in allowing it to recover. He was able to pacify the rest of Persia and move on to the exotic lands of the northwestern Indus valley.


The conquest of the Persian Empire was something that could have easily failed. Even though they relied on tribal levies, were constantly fighting rebellions, and dealt with infighting for the throne, they still were the greatest empire in the world at the time. A Greek city state standing alone stood no chance against it and even the classical hoplites that beat them at Marathon and Plataea would not make it far into the Persian heartland. The Macedonian military was a professional well trained organization and they were able to maneuver in ways that could offset the numbers the Persian king could bring to the field. The traditionally strong and well trained Hetaroi were able to smash through Persian cavalry and the Pezetairoi have had thirty years training in warfare and were able to outfight any conscripted man who was more of a peasant than a soldier. Alexander was also just as great of a tactician as his father. He was able to adapt to situations and make calls that even went against the advice of his officers. He was the only man who could bring his troops 20,000 miles in 12 years.

The Persian Empire fell due to a combination of these reasons. A weakened Persia was not able to be taken advantage of by a separated Greece. The Persians went up against Macedonia, which had not only a well experienced, competent military, but a young charismatic, military genius. Maybe Asia was destined to fall on the day the Temple of Diana burned to the ground, but it was only possible under all of the circumstances lining up perfectly.


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  • Diodorus. Siculus. Bibliotheca Historica
  • Engels, Donald W. Alexander the Great and the Logistics of the Macedonian Army. Berkeley: U of California, 1978
  • Green, Peter. Alexander of Macedon. Berkley, CA: U of California, 1991
  • Heckel, Waldemar (2012-03-29). The Conquests of Alexander the Great (Canto Classics). Cambridge University Press
  • M. Markle, III, Minor (Summer 1977). “The Macedonian Sarrissa, Spear and Related Armor”. American Journal of Archeology (Archeological Institute of America) 81 (3): 323–339
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  • Plutarch. Pericles
  • Plutarch. The Lives of the Noble Grecians and Romans
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  • Quintus Curtius Rufus (1880). Vogel, Theodor, ed. Histories of Alexander the Great. London
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Originally published by Pennsylvania State University under an open access license, republished for educational, non-commercial purposes.