The Sassanid campaign of Alexander Severus was an episode of the Roman–Sasanian Wars (224-363) that saw the Roman Empire ruled by Emperor Alexander Severus (222-235) confront the dominance of the Sasanids, led by Ardashir I (224-241): the war was fought between 230 and 232, originating from an attempted Sasanian expansion into the eastern Roman provinces, and resolved with a return to the status quo ante.
Historical context
Between 224 and 226/227, an important episode changed the fate of relations between the Roman and Persian Empires: in the East, the last Parthian emperor, Artabanus IV, was overthrown after being defeated in "three battles," and the insurgent, Ardashir I, founded the Sasanian dynasty, destined to be the eastern adversary of the Romans until the 7th century. Specifically, between about 229 and 232, Sasanids and Romans clashed for the first time.
On the Roman front, however, the new Severan dynasty that ruled the Roman Empire between the end of the 2nd and the first decades of the 3rd century (from 193 to 235, with a brief interruption during the reign of Macrinus between 217 and 218), and whose progenitor had been Septimius Severus, was now in the hands of a young emperor, Alexander Severus, who a few years later would be killed, proving to be the last descendant. The new dynasty had been born on the ashes of a long period of civil wars, where three other contenders besides Septimius Severus (Didius Julianus, Pescennius Niger, and Clodius Albinus) had faced each other.
Casus belli
The casus belli was the claim by the Sasanids, who considered themselves descendants of the Persians, to possession of the entire Achaemenid Empire, including the territories, now Roman, of Asia Minor and the Near East, as far as the Aegean Sea.
[Ardashir] believing that the entire continent in front of Europe, separated by the Aegean Sea and the Propontid, and the region called Asia belonged to him by divine right, he intended to reclaim it for the Persian Empire. He declared that all the countries in the area, between Ionia and Caria, had been ruled by Persian satraps, starting from Cyrus the Great, who first transferred the kingdom from Media to the Persians, to Darius III, the last of the Persian rulers, whose kingdom was destroyed by Alexander the Great. So according to him it was right to restore and reunite for the Persians, the kingdom they had previously possessed. As a result of this news that came through dispatches from the governors of the East, Alexander Severus was greatly disturbed by the sudden and unexpected news, especially since it came to him after spending a boyhood in an era of peace, and a life in the comforts of a great city [such as Rome]. Therefore, before doing anything, after consulting his advisers, he decided to send an embassy to the "Great King" to try to stop the barbarian's invasion and assess what expectations there were through this letter.
— Herodian, History of the Empire after Marcus Aurelius, VI, 2.2-3.
According to Herodian's account, Alexander proposed to Ardashir that the status quo be maintained, reminding him of Roman victories over the Persians (from Augustus, to Trajan, Lucius Verus, and on to Septimius Severus), but it had no effect on the Sasanian ruler, who soon afterwards took to the battlefield and in 230, penetrated the Roman province of Mesopotamia trying, unsuccessfully, to conquer Nisibis and making several raids into Syria and Cappadocia.
Forces in the field
Sasanids
It is not known precisely how many and what armies were fielded by the Sasanids. Cassius Dio recounts that it was certainly a large army, ready to terrorize not only the Roman province of Mesopotamia, but also that of Syria, west of the Euphrates. Herodian adds that it was equal to the Roman one, thus around 150,000 armed men or perhaps more. The Historia Augusta speaks of the employment in battle of 700 war elephants, 1,800 scythed chariots, and 120,000 cataphracts.
What we know of this army is that it was not permanent like the Roman army, with professional soldiers paid regularly for their work. There was only an eventual division of the final spoils. Rather, there was a system similar to the feudal one, where for each campaign it was necessary to assemble an army from time to time, composed of nobles at the head of their "clans," subjected then under the command of a prince of the royal house. There were therefore no officers expert in weapons who served continuously, nor was there a lasting system of recruitment, as there were no permanent military units, although there were many nobles at the disposal of the Sasanian army. For these reasons, they often hired mercenary armies. They mainly used the bow and the horse in warfare, unlike the Romans who favored infantry, so much so that the Sasanians are said to have grown up from childhood, riding and shooting with arrows, constantly living for war and hunting.
It should be added, however, that unlike the Arsacid Parthians, they tried to keep their contingents under arms for more years during major military campaigns, speeding up the recruitment of their armies, as well as better assimilating the siege techniques of their Roman opponents, which they never really learned from their predecessors.
Romans
It is known that for the Romans, the forces put in charge were the legions and auxiliary troops stationed along the eastern limes, which unfortunately, according to Cassius Dio, were not in an acceptable state of preparedness, discipline, and morale to cope with this new eastern danger, so much so that they thoughtlessly put to death their own governor of the province of Mesopotamia, Flavius Heracleo. Below is a list of the legions and their respective fortresses:
These legions, already present on the eastern front, were joined by others from the Danube and other western regions such as:
as well as some vexillationes from other fronts such as:
The total forces fielded by the Roman Empire along the entire eastern limes may have been around 150,000 Roman soldiers involved or perhaps more (including 30,000 phalangarii, from six legions), half of whom were legionaries, the remainder auxiliaries.
Stages of the war
There are two contrasting accounts of Alexander Severus' Sasanian campaign: one by Herodian, who has no qualms about showing the Roman emperor's mistakes in the conduct of the war and describes a negative situation for the Romans, only to later recount that the Sasanians accepted the status quo ante bellum; on the other hand, in the Historia Augusta, Aurelius Victor's Caesares, Eutropius' Breviary of Roman History and St. Jerome's Chronicon there are accounts of Alexander's glorious victory over his enemies.
231
Emperor Alexander Severus then organized a new military expedition against the Sasanids, enlisting a new legion in Italy, Legio IIII Italica. Herodian reports the speech Alexander made in front of the deployed troops and tells how the soldiers were encouraged by the emperor's words:
I'd like, oh comrades, to give you a customary speech, the speech from which I, speaking to the people, may receive approval, and you, when you hear it, receive encouragement. Since you have enjoyed a period of peace for many years, you may be surprised to hear something unusual or contrary to your imaginations. Brave and intelligent men should pray for things to go well, but they also have to endure whatever happens. It is true that enjoyment of things done for pleasure brings gratification, but good results come mainly from arranging things properly when necessity demands it. Initiating unjust actions is not evidence of good intentions, but it is a courageous act to free ourselves from those who generate dangers when this is done with a good conscience; good results can be expected if one does nothing unjust, but attempts to avoid injustice.The Persian Artaxerxes killed his king, Artabanus IV, and the Parthian Empire turned Persian. He, despising our work and Roman reputation, is trying to assault and destroy our imperial possessions. I have tried to persuade him, by letter, to control his greed and his mad desire to occupy other people's property. But the king, with the arrogance characteristic of barbarians, does not want to stay within his borders and challenges us to battle. We do not hesitate, therefore, to accept his challenge.You veterans will remember the victories against the barbarians under the leadership of Septimius Severus and my father, Caracalla. You recruits, yearning for glory and honor, make it clear that you know how to live in peace with propriety, but make it equally clear that courage is needed for war when necessity demands it. The barbarian is bold against those who hesitate or are cowardly, but he does not hold his own against those who fight; it is not in close combat that they can prevail against us. On the contrary, they believe that any success that leads to victory is the result of looting, after a feigned retreat or escape. Discipline, organization and battle tactics are in our favor, together with the fact that we have always beaten the barbarian.
— Herodian, History of the Empire after Marcus Aurelius, VI, 3.3-7.
After distributing money to the troops, he went to the Senate to make a similar speech and make his intentions public. On the day of his departure for the eastern front (perhaps in the spring of the same year), after attending the ritual sacrifices, Alexander left Rome (231), to reach Antioch, his headquarters.
After crossing Illyricum, where he gathered more troops, he reached Antioch toward the end of the year (231), where he had troops trained in the environmental conditions of the eastern provinces. He then made a final attempt at mediation, offering peace and friendship to Ardashir, which, however, he refused. The latter, in fact, not only sent back the Roman ambassadors empty-handed, but in turn sent a delegation of four hundred mounted archers, looking imposing and richly dressed in gold harness, to intimidate the Romans and invite Alexander to abandon all territories as far as the Bosporus. This provocation irritated Alexander to the point that he had them arrested, later sending them to cultivate lands in Phrygia, but without putting them to death.
232
Source:
As Alexander Severus was preparing to cross the Tigris and Euphrates rivers and lead his army into Sasanian territory, several mutinies occurred among his troops, especially among soldiers from Egypt and those from Syria, where there was an attempt to proclaim a new emperor (a certain Taurinius) and the subsequent disbandment of an entire legion (the II Traiana Fortis), which was reformed shortly afterwards. These defections were quickly discovered and suppressed, although this led the Roman emperor to keep with him only those troops particularly loyal to him.
On the advice of his generals, Alexander divided the army into three parts, keeping for himself the strongest one destined for the center of the attacking front (which was probably to pass through Singara, as reads an inscription of the same year) and which is supposed to have been an advanced "headquarters" of the expedition, while the other two were to march on its sides: one farther north, through the "client" kingdom of Armenia, to Media; another farther south, which, passing through Palmyra, would lead to Dura Europos, then Circesium on the Euphrates, to where this river almost "touches" the course of the nearby Tigris, near the two Persian capitals of Ctesiphon and Seleucia. The idea was to attack the Sasanids from various directions, hoping to find the enemy unprepared for this particular strategy, and believing that forcing the Sasanian army to split up would result in a better tactical outcome in battle for the Roman armies: