Alexander The Great’s Rival, Darius III, Had A Truly Remarkable Army

(Darius III at Issus, c. 1st century BCE, found in Pompeii, [Public Domain] via Creative Commons)


When Alexander the Great began his fateful invasion of the Persian Empire in 334 BCE, the Persians were by no means the underdogs of the war. Even though Alexander had landed an army of around 50,000 men within the Persian Empire, that number was only a small fraction of what the Persian Great King, Darius III, could field in defense of his lands.

Ancient Greek historians loved to embellish numbers. They often drastically increased the scale of battles to make their great accomplishments seem even greater. Nevertheless, even with the most conservative description of Darius III’s military force, the Persians had a distinct manpower advantage against the forces of Alexander the Great.


  (The Battle of Alexander at Issus (cropped), by Albrecht Altdorfer  (1480–1538), [Public Domain] via Creative Commons)


Drawing from all the resources in the Persian Empire, Darius III gathered an army in Babylon, a force he would lead personally against Alexander’s marauding army. The pool of manpower at the disposal of the empire was staggering. From Persia’s heartland in modern Iran, the empire had spread east toward the Indus River Valley of India, as well as westward into Turkey, and south into Egypt. From these lands (also including some of central Asia), a safe estimate is that Darius III could muster around 100,000 infantry and 20,000 cavalry. Along with this impressive army, Darius had access and means to hire immense numbers of mercenaries—he is thought to have employed more Greek soldiers than Alexander the Great.

The military might that Darius III gathered at Babylon in 333 BCE was awe-inspiring. It apparently took a whole day for the army to march before their Great King in parade. Even though much of the Persian army had not yet arrived, Darius III felt he had a great enough force to crush the young Macedonian upstart.

Darius III first met Alexander the Great in the Battle of Issus in 333 BCE. The Pinarus River separated the two forces and the riverbank was rough and elevated on the side of the Persian camp. In addition, Darius had the clear numerical advantage—ancient sources such as Curtius, Diodorus Siculus, Polybius, Plutarch, Justin and Arrian estimate between 300,000-600,000 Persian troops in attendance. Modern estimates, however, reduce the forces of Darius III to around 75,000 men at Issus, which still leaves him with a significant manpower advantage.

Despite the formidable Persian show of force, Alexander the Great did not falter. The Macedonian king did what few generals would suggest—he charged across the river and up the incline to crash against the larger Persian forces and outflank Darius III’s elite center, causing the mighty Persian army to flee. Despite having a smaller force and terrible terrain, Alexander the Great won a decisive victory against Darius III’s truly spectacular army.

Written by C. Keith Hansley.


  • Alexander the Great by Philip Freeman. New York: Simon & Schuster Paperbacks, 2011.
  • Alexander the Great: The Story of an Ancient Life by Thomas R. Martin and Christopher W. Blackwell. New York: Cambridge University Press, 2012.


  1. Alexender, the great was responsible for the destruction of Persian civilization.Darius III with his great numbers of soldiers lost the battle.

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