The Iranian society under the Sasanians was divided-allegedly by Ardašir I, into four groups: priests, warriors (arteštdar), state officials, and artisans and peasants. The second category embraced princes, lords, and landed aristocracy, and one of the three great fires of the empire, Adur Gušnasp at Šiz (Takt-e Solayman in Azerbaijan) belonged to them. With a clear military plan aimed at the revival of the Iranian Empire, Ardašir I, formed a standing army which was under his personal command and its officers were separate from satraps and local princes and nobility. Ardešir had started as the military commander of Darabgerd, and was knowledgeable in older and contemporary military history, from which he benefited, as history shows, substantially. For he restored Achaemenid military organizations, retained Parthian cavalry, and employed new-style armour and siege-engines, thereby creating a standing army (Mid. Pers. spah) which served his successors for over four centuries, and defended Iran against Central Asiatic nomads and Roman armies.
The backbone of the spah was its heavy cavalry "in which all the nobles and men of rank" underwent "hard service" and became professional soldiers "through military training and discipline, through constant exercise in warfare and military manoeuvres". From the third century the Romans also formed units of heavy cavalry of the Oriental type; they called such horsemen clibanarii "mailclad [riders]", a term thought to have derived from an Iranian *griwbanar < *griwbanwar < *griva-pana-bara "neck-guard wearer". The heavy cavalry of Shapur II is described by an eye-witness historian as follows:
"all the companies were clad in iron, and all parts of their bodies were covered with thick plates, so fitted that the stiff-joints conformed with those of their limbs; and the forms of human faces were so skilfully fitted to their heads, that since their entire body was covered with metal, arrows that fell upon them could lodge only where they could see a little through tiny openings opposite the pupil of the eye, or where through the tip of their nose they were able to get a little breath. Of these some who were armed with pikes, stood so motionless that you would have thought them held fast by clamps of bronze".
The described horsemen are represented by the seventh-century knight depicting Emperor Khosrow Parvez on his steed Šabdiz on a rock relief at Taq-e Bostan in Kermanšah. Since the Sassanian horseman lacked the stirrup, he used a war saddle which, like the medieval type, had a cantle at the back and two guard clamps curving across the top of the rider's thighs enabling him thereby to stay in the saddle especially during violent contact in battle. The inventory of weapons ascribed to Sassanian horsemen at the time of Khosrow Anoširavan, resembles the twelve items of war mentioned in Vendidad 14.9, thus showing that this part of the text had been revised in the later Sassanian period.
Heavy Armoured Sassanian Cavalry
More interestingly, the most important Byzantine treatise on the art of war, the Strategicon, also written at this period, requires the same equipments from a heavily-armed horseman. This was due to the gradual orientalisation of the Roman army to the extent that in the sixth century "the military usages of the Romans and the Persians become more and more assimilated, so that the armies of Justinian and Khosrow are already very much like each other;" and, indeed, the military literatures of the two sides show strong affinities and interrelations. According to the Iranian sources mentioned above, the martial equipments of a heavily-armed Sassanian horseman were as follows: helmet, hauberk (Pahlavi griwban), breastplate, mail, gauntlet (Pahlavi abdast), girdle, thigh-guards (Pahlavi ran-ban), lance, sword, battle-axe, mace, bowcase with two bows and two bowstrings, quiver with 30 arrows, two extra bowstrings, spear, and horse armour (zen-abzar); to these some have added a lasso (kamand), or a sling with slingstones. The elite corps of the cavalry was called "the Immortals," evidently numbering-like their Achaemenid namesakes 10,000 men. On one occasion (under emperor Bahram V) the force attacked a Roman army but outnumbered, it stood firm and was cut down to a man. Another elite cavalry group was the Armenian one, whom the Persians accorded particular honour. In due course the importance of the heavy cavalry increased and the distinguished horseman assumed the meaning of "knight" as in European chivalry; if not of royal blood, he ranked next to the members of the ruling families and was among the king's boon companions.
The Sassanians did not form light-armed cavalry but extensively employed-as allies or mercenaries-troops from warlike tribes who fought under their own chiefs. "The Sagestani were the bravest of all"; the Gelani, Albani and the Hephthalites, the Kushans and the Khazars were the main suppliers of light-armed cavalry. The skill of the Dailamites in the use of sword and dagger made them valuable troopers in close combat, while Arabs were efficient in desert warfare.
The infantry (paygan) consisted of the archers and ordinary footmen. The former were protected "by an oblong curved shield, covered with wickerwork and rawhide". Advancing in close order, they showered the enemy with storms of arrows. The ordinary footmen were recruited from peasants and received no pay, serving mainly as pages to the mounted warriors; they also attacked walls, excavated mines and looked after the baggage train, their weapons being a spear and a shield. The cavalry was better supported by war elephants "looking like walking towers", which could cause disorder and damage in enemy ranks in open and level fields. War chariots were not used by the Sassanians. Unlike the Parthians, however, the Iranians organised an efficient siege machine for reducing enemy forts and walled towns. They learned this system of defence from the Romans but soon came to match them not only in the use of offensive siege engines-such as scorpions, balistae, battering rams, and moving towers-but also in the methods of defending their own fortifications against such devices by catapults, by throwing stones or pouring boiling liquid on the attackers or hurling fire brands and blazing missiles.
Heavy Armoured Sassanian Cavalry
The organisation of the Sassanian army is not quite clear, and it is not even certain that a decimal scale prevailed, although such titles as hazarmard might indicate such a system. Yet the proverbial strength of an army was 12,000 men. The total strength of the registered warriors in 578 was 70,000. The army was divided, as in the Parthian times, into several gunds, each consisting of a number of drafšs (units with particular banners), each made up of some Wašts. The imperial banner was the Drafš-a Kavian, a talismanic emblem accompanying the King of Kings or the commander-in-chief of the army who was stationed in the centre of his forces and managed the affairs of the combat from the elevation of a throne. At least from the time of Khosrow Anoširavan a seven-grade hierarchical system seems to have been favoured in the organisation of the army. The highest military title was arghed which was a prerogative of the Sassanian family. Until Khosrow Andoširavan's military reforms, the whole of the Iranian army was under a supreme commander, Eran-spahbed, who acted as the minister of defence, empowered to conduct peace negotiations; he usually came from one of the great noble families and was counted as a counselor of the Great King.
Along with the revival of "heroic" names in the middle of the Sassanian period, an anachronistic title, arteštaran salar was coined to designate a generalissimo with extraordinary authority, but this was soon abandoned when Anoširavan abolished the office of Eran-spahbed and replaced it with those of the four marshals (spahhed) of the empire, each of whom was the military authority in one quarter of the realm. Other senior officials connected with the army were: Eran-ambaragbed "minister of the magazines of empire," responsible for the arms and armaments of warriors; the marzbans "margraves"-rulers of important border provinces; kanarang-evidently a hereditary title of the ruler of Tus; gund-salar "general"; paygan-salar "commander of the infantry"; and pushtigban-salar "commander of the royal guard".
A good deal of what is known of the Sassanian army dates from the sixth and seventh centuries when, as the results of Anoširavan's reforms, four main corps were established; soldiers were enrolled as state officials receiving pay and subsidies as well as arms and horses; and many vulnerable border areas were garrisoned by resettled warlike tribes. The sources are particularly rich in accounts of the Sassanian art of warfare because there existed a substantial military literature, traces of which are found in the Šah-nama, Denkard 8.26-an abstract of a chapter of the Sassanian Avesta entitled Arteštarestan "warrior code"-and in the extracts from the A'in-nama which Ebn Qotayba has preserved in his Oyun al-akhbar and Inostrantsev has explained in detail. The Arteštarestan was a complete manual for the military: it described in detail the regulations on recruitments, arms and armour, horses and their equipments, trainings, ranks, and pay of the soldiers and provisions for them, gathering military intelligence and taking precaution against surprise attack, qualifications of commanders and their duties in arraying the lines, preserving the lives of their men, safeguarding Iran, rewarding the brave and treating the vanquished. The A'in-nama furnished valuable instructions on tactics, strategy and logistics. It enjoined, for instance, that the cavalry should be placed in front, left-handed archers capable of shooting to both sides be positioned on the left wing, which was to remain defensive and be used as support in case of enemy advance, the centre be stationed in an elevated place so that its two main parts (i. e., the chief line of cavalry, and the lesser line of infantry behind them) could resist enemy charges more efficiently, and that the men should be so lined up as to have the sun and wind to their back.
A Sassanian helmet from the siege mines beneath Tower 19, Dura-Europos, in today Syria. It is a rare find of Sasanian military archaeology, and also clearly a prototype for Roman helmets of the 4th century CE.
Battles were usually decided by the shock cavalry of the front line charging the opposite ranks with heavy lances while archers gave support by discharging storms of arrows. The centre, where the commander-in-chief took his position on a throne under the Drafš-a Kavian, was defended by the strongest units. Since the carrying of the shield on the left made a soldier inefficient in using his weapons leftwards, the right was considered the line of attack, each side trying to outflank the enemy from that direction, i.e., at the respective opponent's left; hence, the left wing was made stronger but assigned a defensive role. The chief weakness of the Iranian army was its lack of endurance in close combat. Another fault was the Iranian's too great a reliance on the presence of their leader: the moment the commander fell or fled his men gave way regardless of the course of action.
During the Sassanian period the ancient tradition of single combat (maid-o-maid) developed to a firm code. In 421 CE Emperor Bahram V opposed a Roman army but accepted the war as lost when his champion in a single contest was slain by a Goth from the Roman side. Such duels are represented on several Sassanian rock-reliefs at Naqsh-a Rostam, and on a famous cameo in Paris depicting Emperor Shapur I capturing Valerian.
Sassanian Emperors were conscious of their role as military leaders: many took part in battle, and some were killed; the Picture Book of Sassanian Kings showed them as warriors with lance or sword. Some are credited with writing manuals on archery, and they are known to have kept accounts of their campaigns ("When Kosrow Parvez concluded his wars with Bahram-e Choubina and consolidated his rule over the empire, he ordered his secretary to write down an account of those wars and related events in full, from the beginning to the end").
While heavy cavalry proved efficient against Roman armies, it was too slow and regimentalised to act with full force against agile and unpredictable light-armed cavalry and rapid foot archers; the Persians who in the early seventh century conquered Egypt and Asia Minor lost decisive battles a generation later when nimble, lightly armed Arabs accustomed to skirmishes and desert warfare attacked them. Hired light-armed Arab or East Iranian mercenaries could have served them much better.