1. Structure of the Persian army

The birth, expansion and sustainment of the Persian Empire depended on the bulk and the quality of its army, obliged to carry out offensive or defensive tasks, suppress revolts and assist in the consolidation of the royal power in any possible way.¹ Since kings usually expressed the desire to be surrounded by loyal people, many of the higher army officials were their relatives, such as Mardonius (second half of the 5^th cent. BC). The king himself honoured or punished people or groups of people, depending on their courage and overall performance during a campaign.

The standing Persian army, at least until the 5^th cent. BC, consisted of men of Iranian origin (“Immortals”,² Persians, Medes, Bactrians, Arians). These men were settled not only in Persia, but also in conquered regions, military colonies and garrisons-fortresses.³ However, all men, aged 20 to 50 years old, coming from subordinate, autonomous and allied regions (e.g. Cilicia, Phoenician cities, Arabs) were obliged to take part in the Persian king’s campaigns as conscripts. As a result, the size of the royal army was proportional to the extent of the Persian Empire of the Achaemenids. The count of the expeditionary force of Xerxes I before his campaign against the Greeks indicates the division of the army in national units with regional commanders, subjected to a common (Persian) command. Rarely did exceptions occur, as was the case with certain Greek provinces which did not take part in the Persian wars.⁴

The Persian Empire was divided into military toparchies, which probably correspond to the six military commanders mentioned by Herodotus (484-425 BC). These commanders were in charge of the different nations, the Iranian races and the conscript army.⁵ In special cases, the command of the regional troops of the satrapies was assigned to a karanos. The hierarchy of the Persian army also included generals, myriarchs,⁶ chiliarchs (hazarapatish, military commander of a 1.000-men unit), hecatontarchs and decarchs. The Persians usually assumed the higher positions and the keeping of fortresses and strategic spots.

2. Infantry

According to Herodotus’ information on the national composition, the armour and the uniform of the Persian infantry, the nations of Asia Minor who took part in the Persian wars and the campaign against the Greeks were: the Medes, the Chaldeans, the Paphlagonians, the Phrygians, the Armenians, the people of Lydia, Mysia, Bithynia, Cilicia and Pisidia, the Moschi, the Tibareni, the Macrones and the Mossynoeci. The Persian and Median units of the Persian army in Asia Minor consisted mainly of farmers, whose armour included “Boeotian” (figure-of-eight-shaped) shields and Greek-like breastplates. Generally speaking, every nation used the weapons of its place of origin, which were inferior compared to the armour and training of the Greek hoplites. Since the main bulk of the Persian army consisted of men of Iranian origin, whose basic weapon was the bow, the role of mercenaries (Greeks and the semi-autonomous Chalybes, Taochi, Mardoi, etc.) was upgraded after the 5^th cent. BC. Greek mercenaries also lived in the court of the king.⁷

3. Cavalry

The nomadic origins of the Iranian tribes contributed to the prominent role the cavalry played in the Persian army.⁸ During the early phases of the empire, its cavalry consisted of Persian noblemen and Medes, who used “Spartan” helmets and round “Greek” shields. The cavalry usually contributed to the weakening of the enemy from a safe distance. In the late 5^th and the early 4^th cent. BC, the Paphlagonian cavalry was considered the best unit of the Persian cavalry, whereas the right wing of the army during the battle of Gaugamela consisted of Cappadocian and Armenian cavalrymen.