The greatest problem in the study of Achaemenid warfare is evidential. Almost every narrative source is Greek, written by people the Persians were fighting, and the Persian administrative record that survives — the Persepolis tablets, royal inscriptions, reliefs — is rich on organisation and nearly silent on battle.
What can be established is a system rather than an army: a professional core including the royal guard, satrapal levies raised across an enormous territory, heavy reliance on cavalry and on archery delivered in volume, and a communications infrastructure that allowed forces to be moved and supplied at distances no Greek state could contemplate.
The Greek tradition presents Persian armies as vast, gaudy and brittle. The vastness is rhetorical. The brittleness is a retrospective judgement made by the winners, and the same system conquered and held the largest empire the world had seen for two centuries.
What the evidence supports
Achaemenid armies combined a professional core with levied contingents.
The structure is visible in Greek accounts of order of battle and corroborated by the tribute and delegation reliefs at Persepolis, which show the empire's constituent peoples in distinctive dress and arms.
The royal road system supported military movement.
Herodotus describes the road from Sardis to Susa with staging posts; the Persepolis Fortification tablets independently document the ration-and-travel authorisation system that made it work.
Greek figures for Persian army sizes are unusable.
Herodotus's 1.7 million and Arrian's million are rhetorical. Modern reconstructions vary widely and none is secure.
Archaeology
The Apadana reliefs at Persepolis show delegations from the empire's peoples with their characteristic equipment, and the glazed brick archer panels from Susa show guard troops in detail. Both are official self-representation rather than documentary photography, and should be read as such.
Primary sources
Herodotus, Histories 7.61-99
The catalogue of Xerxes' army: the fullest Greek description of Persian contingents, and simultaneously the source of the impossible numbers.
Xenophon, Cyropaedia
A Greek idealisation of Persian military education rather than a report, but by an author who had served alongside Persian troops.
Achaemenid administration, Persepolis Fortification Tablets administrative archive
Elamite administrative records of rations and authorised travel — documentary evidence for the logistics of the empire, independent of the Greek tradition.
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.
480 BCE
Salamis
A naval battle fought in the straits between Attica and the island of Salamis, and the engagement that broke the Persian campaign.
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.
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.