Carus' Sasanian campaign

Background

The death of Severus Alexander in AD 235 began a half-century of major disruption for the Roman empire, marked by civil and foreign wars and over fifty imperial claimants. Invasions of Shapur I were among the most significant challenges, including the capture of emperor Valerian in 260. Despite unrest caused by Palmyra, relations between Rome and the Sasanians after Shapur's final campaign had been uneventful. Odaenathus' reconquests in Mesopotamia and advances into Persia preceded his death in 270, after which his empire entered instability, leaving the Sasanians unable to pursue conflict with Rome.

War

In early 283, Carus and Numerian moved east toward Persia, leaving Carinus in charge of the western provinces. Carus led a brief campaign against the Sarmatians along the Danube before proceeding to Antioch in spring 283. Carinus was likely elevated to Augustus, possibly connected to his victory on the Rhine. In late spring, Carus led Roman forces from Antioch across the Persian frontiers.

The exact route is uncertain, but he likely crossed the Euphrates, followed it downstream, and continued along the Royal Canal to the Tigris. The army's composition is unknown but may have resembled forces led east by Aurelian in 272. The march toward Ctesiphon was swift with minimal resistance, though more significant resistance occurred along the Royal Canal during the siege of Meinas Sabatha. In midsummer, Carus reached Seleucia and Ctesiphon, capturing both quickly.

Withdrawal

In July, while encamped beyond the Tigris near Ctesiphon, Carus died. Most ancient sources report he was struck by lightning, though a lightning strike in southern Mesopotamia in summer is virtually impossible. Carus was in his sixties, and scholarly hypotheses for his death include assassination, wounds, or natural causes, with no consensus. Upon his father's death, Numerian was declared Augustus and the Romans began to withdraw.

Their return likely followed the Royal Canal and then the Euphrates upstream to Roman territory. An imperial rescript dated to either 8 September or December attests to Numerian's later presence in Syria at Emesa. Numerian's withdrawal was not accompanied by a treaty, leaving relations between Rome and the Sasanians uncertain.

Aftermath

Carinus took the title Persicus Maximus a few months after his father Carus moved on Ctesiphon. In 283, he left Rome for Pannonia, which faced threats from the Quadi. The next year, both Carinus and his brother Numerian added Britannicus Maximus to their titles, probably because of unrest in Britain. After hearing of Numerian's death and Diocletian's takeover, Carinus likely headed to Gaul to gather troops.

Diocletian led the eastern army west along the Danube, sparking a civil war. Carinus beat a rival named Sabinus Julianus but was killed in the summer of 285. Diocletian later made a peace deal with the Sasanians in 287–88, placing the pro-Roman Tiridates III in a possibly divided Armenia, though historians dispute this. That settlement fell apart when fighting resumed in 296.

Carus's campaign was widely praised and compared to earlier Parthian victories, but because the Romans pulled out quickly without a treaty, the overall situation between the empires stayed the same.