Persian Empire
Q & A 6 min read

How Did Alexander the Great Defeat the Persians?

Three things, working together. First, the Macedonian army that Alexander inherited from Philip II was the most effective military force of the Greek world, combining the long-pouched Macedonian phalanx with the companion cavalry. Second, the Persians under Darius III made a series of strategic decisions that, in retrospect, were disastrous: to fight the pitched battles Alexander wanted, on ground Alexander had chosen, and to flee at the critical moment. Third, the Achaemenid imperial system under its last king was structurally fragile in ways the system under Cyrus and Darius had not been, and the eastern satraps proved unreliable when Alexander turned the corner at Gaugamela. The standard modern account is Briant (2002), chapter 14, and Bosworth (1988).

The Macedonian inheritance

The conquest of Persia was a project Alexander inherited, not one he invented. The kingdom of Macedon, under Philip II, had unified most of the Greek city-states, defeated Athens and Thebes at Chaeronea in 338 BCE, and begun to project power into the Aegean. Philip had planned a pan-Hellenic invasion of Persia, partly as a continuation of the Greco-Persian Wars of the early fifth century and partly as a project of Macedonian imperial expansion. Philip’s assassination in 336 BCE cut short the plans, but the project was inherited by his twenty-year-old son.

The force that crossed into Asia in 334 BCE was, by the standards of the Greek world, the most professional and effective army of its time. The Macedonian phalanx, with its longer pike (the sarissa, about 6 metres, longer than the Greek hoplite spear of about 2.5 metres), gave the infantry a reach that the Greek hoplite phalanx did not have. The companion cavalry, an elite force of mounted warriors who were the spearhead of the army, was the arm Alexander used to deliver the decisive blow.

Granicus, May 334 BCE

Alexander met the first Persian satraps at the Granicus River, near Troy, in May 334 BCE. The Persian army, drawn from the satrapies of Asia Minor, was commanded by the satraps of Lydia and Hellespontine Phrygia, and it included a strong force of Greek mercenaries in Persian service. The battle was hard-fought, and Alexander himself was nearly killed — his helmet was cut by the sword of the Persian satrap Spithridates, and his life was saved by the intervention of his companion Cleitus the Black. The Macedonian victory was decisive. The Persian satraps were defeated, the Greek mercenaries were largely killed or captured (Alexander treated the Greek mercenaries as traitors to the pan-Hellenic cause, and refused to take them prisoner), and the way into western Asia Minor was open. Sardis, Ephesus, Miletus, and Halicarnassus fell in quick succession, though Halicarnassus required a significant winter siege 334/333 BCE that demanded extensive Macedonian engineering, not a quick surrender.

Memnon and the counter-offensive

The Persian counter-offensive was, in the early stages, more effective than the Persian government had any right to expect. The Greek mercenary commander Memnon of Rhodes, in Persian service, proposed a strategy of avoiding pitched battles and devastating the Macedonian supply lines — a strategy that might well have brought the invasion to a halt. Memnon captured several cities in the Aegean, threatened the Macedonian rear, and even mounted a naval expedition that retook some of the Aegean islands. By 333 BCE the Macedonian position was becoming precarious, and Alexander was forced to detach part of his army to deal with the Persian naval threat.

Memnon’s death in the summer of 333 BCE, of illness rather than in battle, was the turning point. Memnon was the most capable of the Persian commanders, and his strategy of attrition might well have succeeded had he lived. With Memnon dead, the remaining Persian satraps were unable to mount a coordinated resistance, and the way was open to the Phoenician coast and the great battle of Issus.

Issus, November 333 BCE

Issus was fought in November 333 BCE in the narrow coastal plain of southeastern Anatolia. The Persian army, commanded by Darius III in person, was drawn from the eastern satrapies and included the Immortals, the Indian cavalry, and the Greek mercenaries. The Macedonian army, outnumbered, took advantage of the narrow terrain, which neutralised the Persian cavalry and prevented the Persian army from deploying its full strength. Alexander himself led the decisive charge of the companion cavalry, broke through the Persian centre, and drove Darius from the field. The Persian army was routed, the camp was captured, and the family of Darius III — his mother, his wife, his children — fell into Macedonian hands.

The victory opened the way to the Phoenician coast. The Phoenician cities mostly submitted to Alexander, with the exception of Tyre, which after a seven-month siege in 332 BCE was captured and sacked. The Egyptian satrap surrendered Egypt without a fight, and Alexander was crowned pharaoh in the temple of Amun at the Siwa oasis. The Persian hold on the western half of the empire was broken.

Gaugamela, 1 October 331 BCE

The decisive battle came on 1 October 331 BCE, at Gaugamela, in the Assyrian heartland north of Mosul. The Persian army, again commanded by Darius III, was larger than at Issus, and included Indian elephants, Scythian cavalry, and Greek mercenaries. The Macedonian army was again outnumbered, but its superior discipline and tactics carried the day. Alexander’s decisive charge, with the companion cavalry, broke through the Persian centre, and Darius III fled the field, as he had at Issus. The Persian army was routed, and the way to the Persian heartland was open.

The choice of Gaugamela as the ground of the decisive battle was Darius’s, and it was a bad choice. The plain east of Mosul was flat, dry, and ideal for the deployment of the Persian cavalry and the Persian scythed chariots, but it also gave Alexander the space to use the companion cavalry as a concentrated striking force. A more cautious strategy — falling back on the Persian heartland, refusing battle, forcing Alexander to extend his supply lines — might have produced a different result. Darius was not that kind of king.

The death of Darius III

After Gaugamela, Alexander entered Babylon, Susa, and Persepolis in quick succession. The Greek cities of Mesopotamia submitted, the treasuries of Susa were captured, and the palaces of Persepolis were looted and burned in early 330 BCE. The burning is described in the cluster article on Persepolis; its circumstances remain debated. The Achaemenid state, as a political entity, was at an end.

After the burning of Persepolis, Darius III had fled east, hoping to raise a new army in the eastern satrapies. His flight was intercepted by two of his own people, Bessus, the satrap of Bactria, and Nabarzanes, the commander of the Persian royal cavalry, who arrested him near Hecatompylos in Parthia and murdered him in summer 330 BCE. Alexander, who had been pursuing Darius in the hope of capturing the Great King alive, was deeply affected by the death, and ordered that Darius be buried with full royal honours. The death of Darius III marked the end of the Achaemenid dynasty and the beginning of the Hellenistic period.

Reading

  • Briant, Pierre. From Cyrus to Alexander: A History of the Persian Empire (2002), chapter 14
  • Bosworth, A. B. Conquest and Empire: The Reign of Alexander the Great (1988)
  • Worthington, Ian. Alexander the Great: Man and God (2014)
  • Heckel, Waldemar. The Conquests of Alexander the Great (2012)