The Persian army numbered over a million, according to ancient sources, and naturally, that worked to their advantage at war. Today, experts believe that the Persian army size was in the hundreds of thousands.

So, what was the real size of the Persian army?

Read on to discover the size and different units of the ancient Persian army and its conquests.

How Big Was the Persian Army?

The general estimation of the ancient Persian soldiers was around 120,000. This number did not take into account the soldiers from their allies. Allies like Phoenicia and Mesopotamia provided about 10,000 troops to the Persians.

So, in all, the Persian army averaged 135,000, depending on the battle and the enemy they had to face.

A Brief History of the Persian Army and How It Became Big

The Persian army was not huge right from the onset. It numbered in the thousands before the founding of The Achaemenid Empire (c.550 – 330 BCE).

The Persian Army in the Achaemenid Empire

The founder of the empire, Cyrus the Great, fought and conquered Media, Lebanon, and Babylon. He then united them and drafted their soldiers into his army.

Cyrus the Great then expanded his army to between 120,000 – 150,000 Persian soldiers. He studied the armies of the past including the Medians and Aryans and used their strategies.

The Parthian Empire Military

The Parthian Empire, which came later, then reduced the number to about 50,000 men.  With this number, the Parthians were able to conquer Caria, Cilicia, and Syria.

The Size of the Sasanian Empire Soldiers

The Sasanian Empire again increased the Persian empire military to about 130,000. The empire then organized its army into units that made it fearsome and efficient.

Under the authority of Ardashir I, the military became a professional army. He did not only increase the personnel of the army but also added other military tactics and armor. By including mercenaries from other lands, Ardashir further expanded his army.

The Later Kings Maintain the Same Army Size

All the succeeding Persian kings retained this army size or added a few Persian soldiers for about 400 years. The size of the army enabled Persia to embark on campaigns while defending their cities. Thus, Persia became a superpower due to the size of its army and its efficiency in battle.

The Branches and Units of the Persian Army and Their Roles

The entire Persian soldiers had two major branches: infantry and cavalry. The infantry included the archers, slingers, and swordsmen, while the cavalry had horse and camel riders. The name of the horse riders was asabari and the camel mounters were usabari.

The Persian army had several units made of archers, swordsmen, and cavalry. A unit of 10 men was a dathaba (company). Ten dathabas formed a sataba (battalion), then 10 satabas formed a hazarabam (division) and a group of 10 divisions became a haivarabam (corps).

All these individual units were under the command of high-ranking officers. The King or a nobleman was in charge of the command of the entire army. He was responsible for leading the army to war while his generals implemented diverse tactics.

The Role of the Archers in the Persian Army

The archers were good at hitting their targets and efficient at disorganizing enemy defenses. They were the cream of the Persian army. The archers implored the use of sparabara (huge shields) in defending their lines. Moreover, to protect the archers, the commanders placed them in the middle of the military formation.

In battle, the archers formed a looped hole wall with their shields resting on the ground. From behind these shields, they launched vicious attacks on their opponents. Their short bows were strong enough to propel arrows that could penetrate several layers of armor. The archers inflicted great damage on their enemies even before the actual war began.

At other times, the commanders mixed the archers with the calvary. The idea was to get closer to the enemy to immobilize them. The calvary protected the archers as they both ventured forward. This strategy also kept the enemy forces at bay as none of them ventured to take on the marauding Persian army.

The Role of the Slingers in the Persian Army

The slingers had a limited role which was to cause damage to both the enemy personnel and equipment. The slings had a range of about 1,300 feet and were easy to reload and fire. The missiles for the slings included stones, rocks, and balls of fire. The type of mission determined the type of missile that they would use.

The slingers were essential in siege warfare. They camped at a safe distance outside the walls of their enemies. From there, the slingers released huge boulders against the walls and into the city. The main idea of doing that was to break down the city’s walls and allow the infantry and cavalry to enter.

The Role of the Cavalry in the Huge Persian Army

The cavalry of the Persian army took inspiration from the Scythians. At their founding, they fought with bows and javelins and they were also responsible for ground attacks. Their roles evolved to reflect the complexity of war.

The 5th century saw an upgrade in the weapons of the cavalry from javelins to spears. The cavalry was sometimes sent on reconnaissance missions. They were also deployed as skirmishers to prevent the enemy from seeing their formation. When the army needed to pull a surprise attack on their enemies, they used the cavalry.

The cavalry also chased down retreating enemy soldiers and put them to the sword. Equipped with two palta (spears) the cavalry were part of the vanguard. We should mention here that one palta was for thrusting while the other was for throwing. Finally, the cavalry was a major contributor to the successes of the Persian army.

The Role of the Immortals and Their Number

The Immortals was a specialized unit responsible for guarding the King. They were 10,000 in number and were famous for launching surprise attacks. They earned their name from a strategy that ensured that a fallen Immortal was replaced quickly and efficiently. Thus, they maintained their number.

The Immortals took part in the Battle of Thermopylae where they fought the Greeks. King Xerxes I deployed the Medes against the Greeks but lost. He then sent his famed Immortals to break through the ranks of the Greeks. Inferior weapons and light body armor ensured the defeat of the Greeks.

The Role of the Navy in The Huge Persian Army

Adding to Xerxes army size was the Persian navy. There were about 1,200 ships in the fleet and their main purpose was to fight on the seas. They were pivotal in combating the Greek rebels in 498 BCE. It’s worthy to mention that King Xerxes himself deployed the navy during the invasion of Greece.

The navy fought in the Battle of Salamis against a united Greek front but lost. They suffered huge losses owing that to their big and slow warships.

How the Big Persian Army Came to an End

The big Persian army came to an end with Alexander the Great’s campaigns against the Persian empire. Years ago, the Persians tried to invade the Greeks but failed. The Battles of Thermopylae and Salamis were wars that began the end of the Persian army. This was due to the heavy losses suffered against the Greeks in these battles.

Alexander the Great used lessons from that era to fuel his battles against them. With an army of 50,000 men, Alexander ventured into Persia in 334 BC. By then Persia had ceased expanding but its army was still huge.

Alexander’s troops encountered the Persian army under King Darius III at Issus, a city on the coast. Knowing that he was weaker, Alexander refused to meet his enemies head-on at first. His strategy was simple: use some of his soldiers to draw the enemy towards one flank. When the enemy took the bait and went after that flank, Alexander attacked the gap in the middle.

In the middle were the archers, the strongest offensive force of the Persians. Unfortunately, they were also the weakest link in the Persian army. So, once the gap opened up in the middle, Alexander’s forces struck through the Persian army with ferocity. The fragility of the Persians’ body armor did not help them as the weapons of the Romans sliced through them.


So far, we have covered how the Persian army grew in size and what the role of each unit was.

Here is a recap of what this article has covered:

  • At first, the Persian army had only 1000 men
  • The army grew in size due to the expansion of the kingdom
  • The Persian military consisted of various units, each with its role and commander
  • Due to its size, the Persian army was the most feared
  • By the 5th Century, the number of Persian soldiers had risen to about 150,000
  • The military included infantry, cavalry, and the navy
  • The size of the Persian soldiers started dwindling after the Battles of Thermopylae and Salamis
  • The last straw that severely reduced the number of men in the Persian army was the war against Alexander the Great and his men

The huge number of men in the Persian army was the backbone of the Persian Empire and it spread the frontiers of the Empire, establishing its rule. But due to the casualties suffered at the hand of the Greeks, the empire collapsed, and hence, the Persian army and its numbers fell with the empire as well.


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