Sasanian campaign of Severus Alexander

Historical context

Between 224 and 226/227, the Parthian emperor Artabanus IV was overthrown after three defeats, and Ardashir I founded the Sasanian dynasty. On the Roman side, the Severan dynasty, founded by Septimius Severus after a period of civil wars, was now held by the young emperor Alexander Severus, the last of his line. According to Herodian, Alexander proposed maintaining the status quo and reminded Ardashir of past Roman victories, but the Sasanian ruler rejected this. In 230, Ardashir invaded the Roman province of Mesopotamia, unsuccessfully besieged Nisibis, and raided Syria and Cappadocia.

Forces in the field

The size of the Sasanian army is uncertain. Cassius Dio reports it was large enough to threaten Mesopotamia and Syria. Herodian states it was roughly equal to the Roman force, perhaps around 150,000 men or more. The Historia Augusta mentions 700 war elephants, 1,800 scythed chariots, and 120,000 cataphracts.

The Sasanian army was not a permanent professional force like the Roman one; it was assembled for each campaign from nobles leading their clans under a royal prince, with no continuous officer corps or permanent units. Mercenaries were often hired. The Sasanians emphasized cavalry and archery, while the Romans relied on infantry. Unlike the Parthians, the Sasanians tried to keep contingents under arms longer and improved their siege techniques.

The Roman forces consisted of legions and auxiliaries stationed on the eastern limes, but Cassius Dio notes they were poorly prepared, disciplined, and motivated; they had even killed their own governor of Mesopotamia, Flavius Heracleo. Additional legions were brought from the Danube and other western regions.

Stages of the war

Accounts of the campaign differ: Herodian portrays Roman mistakes and a negative situation, while the Historia Augusta, Aurelius Victor, Eutropius, and Jerome describe a glorious victory. Alexander Severus raised a new legion, Legio IIII Italica, in Italy. After distributing money and addressing the Senate, he left Rome in 231 for Antioch, gathering more troops in Illyricum.

Alexander arrested them and sent them to farm in Phrygia. As Alexander prepared to cross the Tigris and Euphrates, mutinies broke out among Egyptian and Syrian troops; an attempt to proclaim a new emperor, Taurinius, occurred, and Legio II Traiana Fortis was disbanded and later reformed. The defections were suppressed, and Alexander kept only the most loyal troops.

Consequences

The fighting weakened Ardashir's army, and he disbanded it for the winter of 232–233. Alexander, whose health had improved in Antioch, considered the danger over and ended hostilities, partly because of news that the Alemanni had breached the Rhine and Danube limes. The death of Alexander Severus in 235 at the hands of his general Maximinus Thrax, followed by fifty years of military anarchy, gave the Sasanian Empire an opportunity for later revenge, including the occupation of Antioch in 252 and 260.