The Sassanid dynasty overthrew and replaced the Parthian dynasty of the Arcacids during the 3rd century AD, and from then on was the most dangerous rival of the Roman empire. The Sassanid rulers considered themselves the heirs of the Achaemenid kings overthrown by Alexander the Great in 331 B. C. and had a distorted legendary view of history that largely ignored the intervening 600 years , first as irrelevant , then as non-existent . For example, they confused Philip the father of Alexander with the 3rd century AD. Roman emperor of that name! They claimed all the territories of the Achaemenids at their greatest extent, which would have included most of Greece as well as Asian and African provinces that had been Roman for more than three centuries. and demanded that the Romans return these. This attitude made them much more aggressive than the Parthians had been and they frequently launched powerful invasions of the eastern Roman provinces with on the whole more success than failure. The Roman versus Sassanid wars were finally terminated by the Arab conquests of the 7th century AD, which absorbed much of the Byzantine territory and all of Persia
The Sassanid military system was very similar to that of medieval Europe. The only full-time military personnel seem to have been four high officers of state responsible for levying and recruitment. The most important part of the army was the noble cavalry, usually called Clibanarii. This means ” Baking oven men ” in Latin, which in that climate might well be appropriate, but originally derives from “Grive-Pan”, which is old Persian for Warrior. Some men were more or less equivalent to the Palmyran, Roman and Parthian cataphract cavalry. Others were rather lighter armoured and had the bow as their primary weapon, although still possessing Kontos. Horse armour was normal. An all-round protection of leather or thick felt was at first favoured, but this was later apparently superseded by partial metal armour in front only. A roll was kept of men obligated to serve. From the 6th century onward they had to muster to have their equipment inspected and were then paid while the campaign lasted
The mass of the infantry were conscripted peasants. There was no nonsense about a roll. Instead, an official went round to the headman of each village, told him how many men were required, took them from whatever they were doing, and marched them off to be issued with cheap spears and shields. Morale was naturally far from high. The spearmen are reported as forming up in very close order, giving an impression of clustering together for mutual comfort. On one occasion they were actually chained by the ankle to prevent them running away. They were mostly brought along as camp labour and for siege work, but were not entirely useless in battle.
Infantry archers, slingers and javelin-armed skirmishers were more highly regarded. They were almost invariably mercenaries hired from the more out of the way parts of the Persian domain.
Light cavalry armed with bow and javelins were provided by allied tribes such as the Chionitae, Gelani and Albani.
Indian elephants with archers and javelinmen in their towers were another important part of the Sassanid army. They were chiefly useful for their effect on enemy horses and morale.
We have accounts of four pitched battles against the Romans during Julian’s expedition of 363 AD and two more against Belisarius Byzantines. In the first of those against the Romans, the Sassanids had their clibanarii forming a first line, infantry spearmen as a second line and elephants as a third. The Persian cavalry stood to shoot instead of charging with the lance, were charged by the Roman infantry, and after a fierce fight were pushed back and then routed. In the second battle, the Persian front line had its cataphract lancers in the centre with clibanarii on each side. The elephants were drawn up behind. There is no mention of the infantry, who had been very roughly handled in the pursuit after the first battle. The light cavalry may have made a wide outflanking movement to threaten the Roman baggage, but achieved little. The third battle started with a light cavalry attack on the Roman rear. This was beaten off when the emperor brought up light troops to the rescue, but he was fatally wounded by a javelin in the scrimmage. A fierce attack now developed against the centre and left. This was led by charging elephants who got to close quarters but had heavy losses from Roman hand missiles. The impression made by the jumbos was then exploited by cataphract charges supported by the arrows of the clibanarii. The result was a draw with heavy losses on both sides. The fourth battle saw the same Persian tactics used again and was another such draw.
The primary Roman rule of conduct seems to have been to close as early as possible in order to cut down the effect of the Persian archery. Once at close quarters, Roman infantry were obviously more than a match for halted cavalry , and we might speculate that Julian had learned something from the defeat of his own cataphract cavalry by German infantry at Argentoratum in 357 AD.
Deprived of the effect of their archery, the Persians had no option but to charge as in the later battles. Because of the natural desire of a bow-armed warrior to keep at a distance to use his favourite weapon properly, we see these charges being made by the lancer specialists. The Roman infantry must halt and brace to receive the charge, making them a suitable target for archery just before the moment of contact. The scales should have been further weighted in favour of the charge by the residual effects of the sacrificial charge of the elephants However, in most cases the sheer weight of hand-hurled darts, javelins and heavy throwing spears from the Legiones effectively countered the elephants. The use of artillery against elephants was recommended by manuals, but it does not seem to have been used in these battles, possible because the speed of the attack did not allow time to get it into action.
We see the brunt of the Roman fighting being borne by the Legiones, with the cavalry and Auxilia acting as reserves for counterattacking Initial enemy successes.
Belisarius did not have to cope with elephants in his battles and could oppose similar cavalry to the Persian clibanarii. In his first battle against them, he put his infantry in the centre protected by a ditch and used other ditches to canalise and limit attacks on the wings. However, the turning point came when a force of his Hunnic allies posted in ambush attacked the enemy rear. The main lesson of the second battle was never to entrust your flank to an Arab ally. The Arabs left when times got difficult and most of the Byzantine army was rolled up.
Because of their vast quantity of levy infantry, the Sassanids were much better at sieges than the Parthians had been. They had unlimited expendable labour for building siege mounds under fire, plenty of archery for covering assaults, a good supply of captured Roman artillery, and armoured dismounted cavalry for assaulting.
Once, the defenders found themselves being shot at from their rear by a small group of archers that had infiltrated by a tunnel and occupied a tall building, so that artillery had to be shifted to deal with them. However , the Persian camp could be vulnerable at night, and heavy casualties were once caused them by a night sortie of Legionari , some of whom used entrenching tools and axes along with their swords to deal with the more heavily armoured of the enemy, a trick that had been employed previously against heavily armoured gladiators during the 1st century civil wars.
When on the defensive in their own country, the Sassanids supplemented their strongly fortified cities with harassing by light troops, crop and forage burning in the enemy path and delaying actions at irrigation canals by moderate sized forces of all arms. They do not seem to have made much use of river shipping, which gave Julian’s overland transported fleet effective control of the Euphrates.