Achaemenid Armies, Garrisons and Frontiers

From the mid-sixth century to the 330s BC, Achaemenid kings drew on Persian troops, forces from other regions, and local military communities to fight campaigns and hold strategic positions. Commanders had to bring these people, their equipment and their provisions together across a vast territory. What an army looked like depended on where it was going and which forces were assembled for that operation.

Military control changed with conquest, revolt and reconquest. Garrisons at places such as Elephantine guarded routes and crossings, while field armies could be sent back to contested regions.

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Raising forces across the empire

Persian troops formed the core of the royal military establishment, and Medes also served as soldiers and commanders. For particular campaigns, kings called on contingents from subject regions. In his account of Xerxes’ march into Greece in 480 BC, Herodotus, the Greek historian, describes separate groups from Persia, Media, Egypt, Bactria and other parts of the empire, each with its own leader and regional equipment. His list describes that expedition, not a permanent roster for every campaign.

Herodotus identifies ten thousand picked Persian infantry under Hydarnes as the Immortals. In his explanation, the unit kept its stated strength because a soldier who died or fell ill was replaced. This elite group served within a larger army directed by several senior generals, while other commanders led particular peoples and units.

Weapons and mounted troops

Herodotus describes Persian foot soldiers carrying long bows, reed arrows, short spears and daggers, with wicker shields for protection. A wicker shield was made from interlaced rods. Some larger shields could be planted upright so archers could shoot from behind cover. Other contingents carried their own combinations of bows, spears, axes, swords or hide shields; an army’s equipment reflected the troops brought together for that campaign.

Mounted troops added speed for scouting, movement and pursuit. Herodotus notes that only some peoples supplied cavalry, and that their arms and riding animals varied. In Xerxes’ army, Arab camel riders were placed behind the horses because the horses were frightened by camels. The account shows commanders arranging the marching order around the animals as well as the soldiers.

Command and paid service

The king could command an expedition himself or entrust it to senior generals. Herodotus’s account of Xerxes’ land army names commanders for the whole force, leaders of contingents, and officers responsible for groups of thousands and hundreds. This chain connected a royal campaign plan to the separate units that had assembled from across the empire.

A different kind of mixed force appears in Xenophon’s account of Cunaxa in 401 BC. Cyrus the Younger, a Persian prince rebelling against his brother, King Artaxerxes II, hired Greek mercenaries, soldiers serving for pay, who kept their own Greek generals. Cyrus’s Asian troops were under Ariaeus, his second-in-command. As battle approached, Cyrus called to the Greek commander Clearchus to advance against the king’s centre, while Clearchus held his position beside the Euphrates. The arrangement placed the Greek and Asian forces in distinct parts of the battlefield under different immediate commanders.

The soldiers’ pay was negotiated. When Cyrus’s Greek troops demanded more, he promised one and a half darics a month instead of one; a daric was a gold coin. Xenophon’s episode shows how a ruler could secure the service of hired troops through a specific pay agreement, alongside the leaders and units supplied for other parts of the army.

Feeding and moving an army

Large campaigns needed food for soldiers and fodder for horses and pack animals. Before Xerxes’ invasion of Greece, Herodotus says Phoenicians and Egyptians were assigned transport and provisioning work. Grain and other supplies travelled in merchant ships and transports to depots at places along the route, including Doriscus and Eion. Stores placed ahead of the marching army reduced the distance its wagons and pack animals had to carry every day.

Land routes and coastal passages worked together. Xerxes’ army marched overland while the fleet followed the coast, with orders for the ships to meet the army near the headland of Sarpedon in Thrace. At Doriscus, ships were hauled onto the beach to rest while Xerxes arranged and reviewed the troops. The control of roads and other routes connected such mustering places, store depots, crossings and garrisons.

Garrisons and changing frontiers

Egypt’s changing status shows how frontiers could shift over the life of the empire. Cambyses conquered the Nile valley in 525 BC. The first period of Persian rule ended around 402 BC; after a stretch of native dynasties, Artaxerxes III reconquered Egypt in 342 BC. Persian authority there lasted only briefly in this second period, ending with Alexander’s conquest in 332 BC.

Elephantine, an island at modern Aswan, guarded the Nile’s first cataract, a stretch of rocky rapids, and the main route south toward Nubia. Its garrison was an important frontier post. Aramaic records show that soldiers in the Jewish military community received monthly pay partly in cash and partly in kind, including cereals and oil. This local record makes the maintenance of a garrison concrete: military service depended on regular provisions as well as a command structure.

Farther north-west, Meydancık was a hilltop fortress in western Cilicia, on the southern coast of Anatolia. An Aramaic inscription identifies it in the Achaemenid period as the fortress of Kirshu. The occupation included a massive fortified entrance and unusual reliefs showing figures in Persian court dress approaching a spear-bearing court figure. Its stone entrance and reliefs show how a fortified position could express royal authority well beyond the Persian heartland.

Fleets and naval service

Naval service brought ships and crews from Phoenician, Cypriot, Egyptian and Greek-speaking coastal communities into Achaemenid campaigns. Fleets moved soldiers and provisions along coastlines, protected maritime approaches and fought when opposing forces met at sea. Their commanders coordinated with land forces at agreed landing places and rendezvous.

The fleet’s role continued beyond Xerxes’ invasion. In 394 BC, the Persian commander Pharnabazus and the Athenian Conon led a combined force that defeated Sparta off Cnidus. Xenophon describes Pharnabazus with the Phoenician ships and Conon commanding the Greek squadron. The victory was followed by operations against Spartan garrisons on islands and coastal cities.