The Achaemenid Persian army that faced the Greeks in the Persian Wars (499-449 BCE) was the product of a half century of evolution as the House of Achaemenes expanded into new territories and merged the fighting styles and martial technologies of conquered peoples into its army. Cyrus the Great’s (r.559-530 BCE) army was constituted much differently than that of Persian host which accompanied the Great Persian king Darius I (r.522-486 BCE) on his Punitive Expedition against the Greeks in 490 BCE, a campaign that culminated in the Athenian victory at Marathon and a second, and more devastating, Persian Expedition (480-479 BCE) led by Darius’ son, Xerxes (r.486-465 BCE). This remarkable multinational army helped these three Great Kings carve out the largest empire in world history to date, consisting of over three million square miles of territory on three continents, with over fifty million inhabitants.

The early Achaemenid armies were not professional fighting forces as much as they were royal levies (kara in Old Persian) made up of noble kinsmen and their retainers. The Persian army became more sophisticated in the late seventh century BCE when the Medes (heavily influenced by Assyrian martial practices) began to dominate their southern neighbor, transferring a new military organization and professionalism to the Persian military. The Medes organized their army into a professional standing army (spada) divided into separate contingents on an Assyrian model. The Persian spada consisted of infantry (pasti), cavalry (asabari, meaning "horse-borne" and occasionally usabari meaning "camel-borne"), and charioteers.  The core troops of the spada would continue to be ethnic Persian or Medes, even as the army grew to contain foreign contingents from conquered regions in Anatolia, Mesopotamia, the Levant, Egypt, and Central Asia.  It is also likely that the Persians benefitted from Assyrian siege warfare techniques through this Median inheritance, including the use of the battering ram, siege towers, and sapping.

When Cyrus became king around 559 BCE, the Persian army he commanded was a combined-arms force that emphasized massed missile fire to soften up enemy formations followed by cavalry strikes. Early Achaemenid battle doctrine borrowed heavily from the Assyrians and placed infantry archers protected by wicker shield-bearing infantry spearmen in the center formation, flanked by Persian and allied cavalry units. Together, Persian spearmen and archers were known as sparabara or archer-pairs (spara is Old Persian for large shields and the troops that carried the spara were called sparabara or “shield bearers”). The Assyrian archer-pairs were composed of two different units of troops of equal strength, operating together in a tactical formation comprised of only a single line of archers behind a single line of shield-bearers.  However, when historians find sparabara operating in the Persian army, both types of troops are operating in the same ten-man file or dathabam at a ratio of one shield-bearer for every nine archers.  Furthermore, Persian shield-bearers, unlike their Assyrian counterparts, were now armed with short thrusting swords (akinakes) and six-foot long thrusting spears to better protect the file of nine archers behind him. This new arrangement enabled the ratio of archers-to-shield men to be significantly altered in order to give a heavier concentration of arrow fire. The shield-bearer carried a large rectangular shield, similar in dimensions to the medieval pavise that protected archers and crossbowmen. This large Persian shield was formed from a larger rectangular piece of thick leather into which osiers (twigs) were woven vertically and parallel to one another when the leather was still supple and uncured.  When the leather hardened, the resulting wicker shield was both light and strong. This large shield could be propped with others of its kind to form a makeshift shield wall at the battle front, freeing the shield-bearer to become a dedicated spearman. Protected by the spearmen were infantry archers wielding powerful recurve bows, probably composite bows due to prolonged contacts with steppe peoples.  In fact, the Persians preoccupation with light infantry archers supported by cavalry meant that they did not develop true heavy infantry during the time of Cyrus. Later, Persian Great Kings would hire Greek heavy infantry mercenaries to supplement their tactical mix. Alexander III of Macedon (“the Great,” r.336-323 BCE) faced Greek hoplites in Persian service at the battle of Granicus River in 334 BCE and the young Athenian general Xenophon ‘s (c.430-354 BCE) “10,000” served a Persian pretender in his loss at Cunaxa in 401 BCE.

The first Persian cavalry was most probably modeled after neighboring Median or Scythian light cavalry, Indo-European horse peoples with extraordinary skills as mounted archers. However, Cyrus recognized the necessity for a contingent of indigenous Persian cavalry if he were to deal successfully with the cavalry-using Medes, Lydians, and eastern Iranian tribes. He organized and financed the first Persian cavalry himself using war treasure and land gained in campaigns in the west.  Cyrus gave land to Persian nobles known as “equals,” and then required them to use this land to support the cost of cavalry from then on, creating the one of the first mounted aristocracies in history.  Fifteen thousand Persian noblemen were given the honorary title of Huvaka or “Kinsmen.”  Cyrus went as far as to require the Huvaka or Kinsman Cavalry to ride everywhere and made it disgraceful for these noblemen to be seen on foot. From these 15,000 mounted noblemen Cyrus created an elite regiment of 1,000 cavalry to serve as his personal cavalry.  Although not a proficient shock cavalry during Cyrus’ reign, the Huvaka would eventually develop into a well-armored heavy cavalry famous for their shock tactics.  Quality heavy cavalry would continue to be a hallmark of the Persian art of war for another twelve hundred years through the Parthian (247 BCE-224 CE) and Sassanian (224-651 CE) periods, with Sassanian elite heavy cavalry (Savaran) used as a primary fighting arm in their campaigns against the Byzantines and Arab and Turkish Muslims. To supplement the newly formed Huvaka, Cyrus and his successors employed allied tribal light cavalry from the Iranian Plateau (Dahae, Sagarthian, and Mardian) as mounted archers, scouts, and as pursuit troops.  

The Persian army during the reign of Cyrus was organized using a decimal system into regiments of a thousand men, in a system very similar to the later Mongol military organization, made famous by Genghis Khan. The Old Persian term for these regiments was hazarabam meaning “thousand.”  Each hazarabam was further divided into ten sataba of a hundred men, and again into ten dathaba consisting of ten men each. The dathaba was the basic tactical unit in the infantry and was organized by files on the battlefield. On campaign ten hazarabam regiments formed a myriad (a Greek word, as the Old Persian word has not survived) of 10,000 men, the largest maneuver unit in the Persian army. The most celebrated of these myriads was the Great King’s “Immortals” (Amrtaka in Old Persian). The Greek historian Herodotus (484-425 BCE) tells us that the name comes from the division always being kept up to full strength.  The Immortals were drawn from the best troops in Persia and Media, both noble and non-noble. Among these 10,000 men were elite aristocratic regiments known as the “Apple bearers” (for the golden or silver apples or more likely pomegranates on the butt of their spears) who served with the Kinsman Cavalry as the Great King’s bodyguard. Herodotus describes the unique uniform and panoply of the Immortals:

“On their heads they wore tiaras, as they call them, which are loose, felt caps, and their bodies were clothed in colorful tunics with sleeves (and breastplates) of iron plate, looking rather like fish-scales. Their legs were covered in trousers and instead of normal shields they carried pieces of wickerwork. They had quivers hanging under their shields, short spears, large bows, arrows made of cane, and also daggers hanging from their belts down beside their right thighs.” 

Herodotus makes special note of the lack of armor on these elite troops, especially when compared to the more familiar Greek hoplites defending his homeland during the Persian Wars.

Persian boys began their military instruction quite young in a manner reminiscent of Greek Spartan education in the Agoge. His formal education began at the age of five and lasted until he was twenty, with the child and adolescent training in companies of fifty in physical, cultural, and martial skills. He learned how to swim, march, and run long distances, as well as stand long watches. True to his steppe origins, he also learned how to groom a horse, tend cattle, and till the land. During this decade and a half, the young man trained in archery (on foot and mounted), javelin and spear fighting, and sword fighting with akinakes. At the age of twenty, he was integrated into the Persian army to complete his formal training as either infantry or cavalry, with elite forces training as both. The comprehensive nature of this martial training is summed up in the words of the Great King Darius I, who boasted:

"Trained am I both with hands and with feet. As a horseman I am a good horseman. As a bowman I am a good bowman both afoot and on horseback. As a spearman I am a good spearman both afoot and on horseback."

This form of training on foot and on horseback is reflective of Persian society as a whole, a culture with a strong cavalry tradition who adopted the ways of civilized warfare as it conquered its way across the Near East.  And to maintain that large empire, military readiness was emphasized, with all able-bodied Persian males required to serve active-duty and then as militia until the age of fifty. There is also evidence of land grants and pensions for retired soldiers. 

The Immortals division is the best known of all Persian military units because of their participation in the Persian War against Greece.  Herodotus describes in some detail this myriad’s role in the Thermopylae campaign in 480 BCE.  However, the Immortals fought with distinction in Cyrus’ conquest of Babylon in 547, Cambyses’ campaign in Egypt in 525, as well as Darius’ invasions of India and Central Asia in 520 and 513.  The Immortals continued to serve Great Kings during the entire Persian Empire and were present as Darius III’s bodyguard during his campaigns against Alexander the Great in the 330s (even famously whisking Darius away from the battlefields of Issus and Gaugamela). This storied division was resurrected by the Sassanian Persians as the Zhayedan hundreds of years later, although as a cavalry rather than an infantry division.  Indeed, so powerful was the “Immortals” legacy that this title was even used twice by the Byzantines in the tenth and eleventh centuries for their elite units (Athanatoi or “Without death”). 

By Cyrus’ death in 530 BCE, the Persian army was already a multinational fighting force that would only grow in its international composition with the conquests of Cambyses and Darius.  Persians and Medes aside, most of the infantry used by Cyrus’ successors were levied from the subject peoples, with each contingent using their own national arms, organization, command, control and communication, and tactics. Herodotus records thirty-five different nationalities in Xerxes’ army for the invasion of Greece in 480 BCE. Most of these contingents were archers, although Herodotus implies the Lydian’s “equipment was not very different from the Greek” (perhaps implying the Persians may have had a small mercenary hoplite force in their service).  Thracians also accompanied the Persians on this expedition as skirmishers, carrying their own “javelins, bucklers, and small daggers.” Subject peoples would continue to serve Persian Great Kings for the duration of the Persian Empire, as the composition of the Persian army faced by Alexander during his own Persian campaigns (336-330 BCE) illustrates.

To provide better oversight over his massive empire, Darius I reorganized the empire from dozens of client kingdoms into twenty Satrapies (provinces) connected by a new road system to move troops during wartime and facilitate trade between regions within the empire during peacetime. Loyal Persians or notable allies were placed as governors (Satraps) of these new provinces.  The main artery of this new road system, known to history as the “Royal Road” or King’s Road” ran from Sardis (modern Sart in western Turkey) to Susa (modern Shush in southwestern Iran), a distance of 1,600 miles through secure inhabited country.  Herodotus explains that a Persian army could travel this distance in just ninety days, an impressive display of strategic mobility.  Darius ordered 112 staging posts placed along the Royal Road’s length so that royal mail could be sent via mounted messengers.  This classical “pony express” could traverse the length of this road, riding day and night under favorable conditions, in less than a week. The Persian Royal Road was this first strategic highway in western civilization.  

Cyrus’ campaigns in the west won him the Mediterranean coastlines of Anatolia and the Levant, but he did not build a navy during his reign.  His son and successor, Cambyses II (r.530-522 BCE) recognized the importance of a navy when he decided to invade Egypt in 525 BCE, with Persian soldiers (most of whom could not swim) serving as marines, while oarsmen were recruited from the citizenry of Phoenicia. Although details concerning the constitution of early Persian fleets are scarce, historians believe that flotillas were organized into squadrons of 300 ships (perhaps modeled after the Corinthian navy’s structure, a leading Hellenic sea power of the day). With Egypt folded into the Persian Empire, the world’s first imperial navy patrolled the coastline of the entire eastern Mediterranean and had only one major rival, the Greeks.  This rivalry would spark into open warfare after a Greek rebellion in Western Anatolia in 499 BCE pulled Athens into confrontation with Cambyses’ successor Darius, initiating the Persian Wars. 

Suggested Readings:

Primary sources

Strassler, Robert B. ed. The Landmark Herodotus: The Histories. Anchor, 2009.

Secondary sources

Carey, Brian Todd, Joshua B. Allfree, and John Cairns. Warfare in the Ancient World. Pen and Sword, 2006.

Cook, J.M. The Persian Empire. Schocken Books, 1983.

Farrokh, Kaveh. Shadows in the Desert: Ancient Persia at War. Osprey, 2009.

Wiesehofer, Josef. Ancient Persia. I.B. Tauris, 2011.