In 230, Ardashir (Artaxerxes) felt confident enough to invade Roman Mesopotamia. He laid waste to the country and threatened Syria, though he failed to take Nisibis. The Persian invasion may have been just a probing attack instead of a full-scale assault, but it was serious enough to draw the emperor to the East. First, he sent envoys and tried to negotiate with his adversaries. It soon became clear that his opponent was keen to restore the Achaemenid Persian Empire that had been destroyed by Alexander the Great in 331 BCE. Ardashir – at least according to the biased Roman sources – basically claimed all the territories that had once been under Persian rule. This was, of course, not acceptable for Alexander the Great’s namesake. Severus Alexander arrived in Syria with his mother, probably in 231. Now that diplomacy had failed, the emperor began mobilising his forces near Antiochia. New troops had already been recruited in Italy and other parts of the Empire. The Historia Augusta claims Alexander had created an elite corps of men with silver and golden shields (argyroaspidas et chrysoaspidas), and had formed a phalanx of 30.000 men which he called his phalangarii. These men seem to have been ordinary legionaries from six legions, equipped like other Roman legionaries, but receiving a higher pay after the war.
Alexander was now ready for war, but tried to give diplomacy another chance. Ardashir refused to speak to the Roman envoys, and sent his own envoys to Alexander instead. They made demands that were clearly disproportionate. Herodianus writes:
“The envoys said that the great king Artaxerxes ordered the Romans and their emperor to withdraw from all Syria and from that part of Asia opposite Europe; they were to permit the Persians to rule as far as Ionia and Caria and to govern all the nations separated by the Aegean Sea and the Propontic Gulf, inasmuch as these were the Persians’ by right of inheritance.”
Alexander decided to give the Persian envoys part of what they wanted, figuratively speaking. He had the envoys arrested and sent to Phrygia (once part of the Persian Empire), where farmland was assigned to them to work on. The furious Roman emperor now began his counter-offensive.
Alexander – or rather: his staff – divided his forces into three separate columns. The first column was to march from Antiochia to Edessa, then through Armenia and attack the satrapy of Media. The second column received orders to follow the Euphrates in the direction of Ctesiphon (which is on the Tigris), while the third, commanded by the emperor himself, took the middle route between the Euphrates and Tigris rivers. The ultimate goal of the expedition is not mentioned in our sources, but some historians have speculated that it may have been the Persian heartland near Susa. The first division had great difficulty getting through the Armenian mountain range, but nevertheless managed to reach Media. The countryside was pillaged and Persian counterattacks were largely ineffective, as the rocky terrain greatly favoured the Roman infantry. Ardashir decided not to focus on Media, but to turn his attention to the second Roman column, which was marching along the Euphrates.
This second column should have been covered by Alexander’s third column, but it was not. While the commanders still believed their flank was secure, the second column suddenly found itself opposite the main Persian army. The Romans were badly outnumbered, and to make things worse, Alexander did not come to their rescue with his own troops. The second Roman column was massacred. Herodianus writes that:
“The king attacked it unexpectedly with his entire force and trapped the Romans like fish in a net; firing their arrows from all sides at the encircled soldiers, the Persians massacred the whole army. The outnumbered Romans were unable to stem the attack of the Persian horde; they used their shields to protect those parts of their bodies exposed to the Persian arrows. Content merely to protect themselves, they offered no resistance. As a result, all the Romans were driven into one spot, where they made a wall of their shields and fought like an army under siege. Hit and wounded from every side, they held out bravely as long as they could, but in the end all were killed.”
There may of course have been a few survivors, but the battle had been a staggering defeat for Alexander, who had shown a lack of skill as a general. His soldiers were furious and felt betrayed by their emperor. To make things worse, Alexander fell ill and ordered a full retreat back to Antiochia. He also recalled the column that was still fighting in Media. This part of the army suffered heavily on the way back, not just from enemy attacks, but mostly from frostbite, as winter had already set in. To add insult to injury, Alexander’s own column suffered numerous casualties as well on its way back to Syria. The emperor had to dig deep into his coffers and distribute money among his soldiers to remain assured of their loyalty.
The expedition had been a disaster, but according to Herodianus, the Persians had suffered heavy losses as well:
“Though the barbarians seemed to have conquered because of their superior strength, they were exhausted by the numerous skirmishes in Media and by the battle in Parthia, where they lost many killed and many wounded. The Romans were not defeated because they were cowards; indeed, they did the enemy much damage and lost only because they were outnumbered. Since the total number of troops which fell on both sides was virtually identical, the surviving barbarians appeared to have won, but by superior numbers, not by superior power. It is no little proof of how much the barbarians suffered that for three or four years after this they remained quiet and did not take up arms.”
It does indeed seem possible that Persian losses in Media were considerable, and the encircled Romans near the Euphrates may have taken quite a few enemies with them to Hades, but in the end the Romans were the true losers of this war. Alexander immediately mobilised new troops and prepared for an invasion that did not come. Ardashir for the next few years decided to focus on consolidating his power in his home country. But he had certainly not forgotten his expansionist ambitions.
– Adrian Goldsworthy, The Fall of the West, p. 88-91.