Achaemenid armies were assembled rather than maintained. A professional core around the king and the satraps was expanded for campaigns by levies from the provinces, each contributing troops in their own equipment and fighting style — which is what produces the catalogue of peoples in Herodotus and the delegation reliefs at Persepolis.
The tactical emphasis differed from Greek practice. Persian infantry combined a wicker or hide shield with the bow, and the intended battle was one in which massed archery disordered an enemy before cavalry exploited it. Against heavy infantry on constricted ground this failed repeatedly; on open ground against opponents without an answer to cavalry it worked for two centuries.
The organisation Herodotus reports is decimal — units of ten, hundred, thousand and ten thousand. It is plausible and is not independently confirmed in the Persian record.
What the evidence supports
Contingents served in their own equipment.
Herodotus's catalogue describes distinct arms and dress by people, and the Persepolis reliefs corroborate the diversity, if not the specific battle order.
The system depended on imperial logistics.
The Fortification tablets document authorised travel and ration issue across the empire — the administrative machinery that made large-scale movement possible.
Greek accounts of Persian tactics are shaped by Greek victory.
The narrative of brittle, over-large Persian armies is written by the winners of a handful of engagements, and is a poor guide to a military system that conquered from the Aegean to the Indus.
Primary sources
Herodotus, Histories 7.61-99, 9.20-70
The catalogue of contingents and the account of Persian tactics at Plataea.
Xenophon, Anabasis 1
A Greek mercenary's first-hand view of a Persian royal army on campaign at Cunaxa.
Achaemenid administration, Persepolis Fortification Tablets administrative archive
Documentary evidence for imperial logistics.
Battles
490 BCE
Marathon
An Athenian and Plataean hoplite force defeated a Persian expedition on the coast of Attica, and the Greek world learned that a Persian army could be beaten.
480 BCE
Thermopylae
A Greek force held a coastal pass in central Greece for three days against the army of Xerxes, and was destroyed when the position was turned by a mountain path.
479 BCE
Plataea
The largest hoplite battle of the Persian Wars, which destroyed the Persian field army in Greece and ended the invasion.
334 BCE
The Granicus
Alexander's first battle in Asia, fought at a river crossing against the satraps of the western provinces, and the engagement that opened Asia Minor to him.
333 BCE
Issus
Alexander's first battle against Darius III, fought on a narrow coastal plain that neutralised Persian numbers, and after which the Persian royal family fell into Macedonian hands.
331 BCE
Gaugamela
The decisive battle of the Persian war, fought on ground Darius had chosen and prepared, and after which the Achaemenid empire had no field army left.
53 BCE
Carrhae
A Roman army was destroyed in open desert by Parthian horse archers and cataphracts, in the clearest ancient demonstration that heavy infantry has no answer to mobile missile cavalry.
How to read the evidence labels
- Evidence level: Documented
- Supported by a named primary text or by excavated material evidence.
- Evidence level: Probable
- Supported by strong inference that most specialists accept.
- Evidence level: Disputed
- Substantial specialist disagreement exists; competing readings are stated.
- Evidence level: Literary
- Belongs to poetic or mythological construction rather than to history.
- Evidence level: Mythological
- Belongs to shared religious or mythic tradition rather than to any single text.
- Evidence level: Unknown
- The available evidence is insufficient to decide.
These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.