Military
Information about the Parthian military is fragmentary and derives from a variety of textual and archaeological sources. Each of the kings and wuzurgan were expected to contribute cavalrymen to the army, which formed its backbone, as well as conscripted foot soldiers.[874] In addition, the Arsacid kings employed a variety of Central Asian mercenaries to ease dependence on the levies of the wuzurgan, and indeed to preserve their independence from them.[875] The Parthian military was perfectly adapted to warfare conducted on the steppes of Central Asia and the desert plains of Mesopotamia and Iran.[876] The cavalry formed the core of the Parthian army and was divided into two divisions.
The first were lightly armored archers, armed with a powerful recurve bow, in manner similar to the Central Asian nomads that the Parthians periodically faced. Our textual sources indicate that these mounted archers never engaged in close combat, but were used to encircle, contain, and generally wear down the enemy. The second division consisted of heavily armored lancers with horse and rider covered from head to toe with lamellar armor. The heavy cavalry would break the weakened enemy through a frontal charge.[877] While Parthian military organization and battle tactics indeed kept pace with those of their Central Asian adversaries and were applied with success against Rome, archaeological evidence indicates that the early Parthians appropriated and adapted aspects of Hellenistic fortification design and defensive heavy weaponry.The Sasanians are more famed for building long land walls, but the Arsacids too created an impressive chain of fortified cities and fortified outposts protecting frontiers and major cities.[878] The Parthians fortified their most important cities in eastern Iran, such as Nisa, Merv, and Hecatompylos, with trapezoidal mud walls that incorporated modified Hellenistic defensive design.[879] As part of the later Parthian efforts to assert control over Mesopotamia, they rebuilt and strengthened defunct cities like Assur and Nippur, whose venerable yet defunct ziggurat and Ekur sanctuary were partially razed, rebuilt and transformed into a fortified citadel and palace complex.[880] The western foothills of the Zagros Mountains, a region that received renewed attention in the Sasanian period, controlled access to the northern Iranian Plateau and was guarded by many Parthian fortresses, and it is possible that parts of the 115-kilometer-long Gawri Wall were started in the Parthian period as well.[881]
Members of a class of commoners that Plutarch refers to as pelatai and Justin as servi were attached to the nobles and owed them military service.
Lower on the social hierarchy, a class of serfs, referred to by Plutarch as douloi and Pompeius Trogus/Justin again with the word servi, labored under the control of the nobles and on their estates but enjoyed minimal autonomy and were evidently not among those trained as horsemen. According to the latter, the pelatai/servi were required to serve as cavalrymen under the nobles when called and were trained and equipped by them in exigency. The text records that the Parthian army of 50,000 horsemen that defeated Antony consisted of 400 nobles (liberi) with the rest servi. While the numbers might not be completely accurate, the relative proportions provide an idea of social structure within the Parthian core of the empire. The Arsacid king's Central Asian mercenaries required a large amount of money, which the king generated through conquest in the early empire, and increasingly through trade.[882]The Sasanian army inherited the organization and techniques ofthe Parthian military.[883] Mounted archers and heavy cavalry were its most important components. Archaeological evidence from sites such as Dura Europos indicates that under the Sasanians the heavy cavalry incorporated chain mail and plate armor. In the early empire the wuzurgan and client kings supplied the cavalry. The reforms of the sixth century and introduction of the state-supported aswaran significantly changed the recruitment structure of the heavy cavalry, creating a core of the army who depended directly on the king of kings for their equipment and pay.[884] In addition, in the late empire the king of kings recruited a variety of Central Asian peoples to serve as cavalry to further lighten dependence on the wuzurgan. Throughout their history, Sasanian armies made use of elephants to great effect against the Romans.[885] Foot soldiers did not play a large role in the traditional Sasanian battle formation on their preferred terrain, although when fighting in the mountainous regions of the Caucasus, they proved they could be adaptable.
By the fifth century the Sasanians built and maintained a series of fortifications and long walls along their northern borders, which, from a broader Eurasian perspective, joined a larger 10,000 kilometer network of built and natural defensive barriers created or leveraged by multiple sedentary empires over the course of the first millennium to defend against nomadic incursions.[886] The most important were in the Caucasus at the Daryal pass and Darband and in northeastern Iran, where the Sasanians built the Gorgan Wall and Tammishe Wall. The Daryal Pass (the “Alan Gate”) was the main invasion route through the central Caucasus, and the walls at Darband (the “Caspian Gates”) and Ghilghichay sealed off the passage along the western Caspian shore.[887] The Gorgan Wall was a 195-kilometer brick wall that led from the southeastern shore of the Caspian to the northeasternmost arc of the Alborz Mountains to protect the Gorgan plain.[888] A series of rectangular forts punctuated it and housed border garrisons. The Tamisa Wall led 10.5 kilometers from the southern shore of the Caspian Sea to the Alborz Mountains, providing another barrier between the Gorgan plain and southern Caspian coast. The kings of kings supplied lands to support the border guards, and funds for the upkeep of these defenses were a constant bone of contention between the Persians and Romans.[889] In the foothills of the western Zagros, the Gawri wall runs 115 kilometers in an arc from north-southwest to protect incursions from the west along the Great Khorasan route. These frontier fortifications functioned as part of a larger empire-wide system of forts, fortified cities, royal estates and major temples, which not unlike those of the Seleucid and Parthian empires, acted as nodal points that controlled routes of communication, projected power into the countryside and facilitated mercantile and agricultural investment. As seen at the regions as diverse as Mesopotamia (including around Ctesiphon) and the plains south of the Upper Caucasus and northeastern Caspian frontiers, the forts or fortified cities often protected investments in irrigated landscapes, whose canals could also simultaneously act as linear barriers and corridors in concert with urban circuit walls or the frontier land walls.[890] The Persian army became very skilled at siegecraft as well, and could counter the best Roman frontier fortifications and counter-siege techniques, even employing “chemical warfare.”[891] At the end of the empire, the Roman and Persian armies were very similar to each other, and the Persian army matched and often beat the Romans in logistical organizational capacity and technological know-how.