Odaenathus' Sasanian campaigns

Forces in the field and Background

Odaenathus assembled the Palmyrene army and Syrian peasants, then marched north to meet the Persian emperor returning to Persia. According to Zosimus, Odaenathus's army in 260 included his own Palmyrene troops and remnants of Valerian's Roman legions, possibly aided the Romans during the Battle of Edessa. Troops based there may have been loyal to Gallienus and chosen to join Odaenathus. Later historians such as Festus and Orosius mentioned the peasant element; Orosius called the army "manus agrestis syrorum," leading Edward Gibbon to portray it as a "scratch army of peasants."

Richard Stoneman rejected this, arguing that the success against Shapur I and later victories under Zenobia could hardly come from an ill-equipped, untrained peasant army. He interpreted agrestis as denoting troops from outside urban centres, concluding that Odaenathus levied his cavalrymen from regions around Palmyra where horses were bred and kept. Roman Emperor Valerian had led forces against Shapur I's invasion starting in 254, possibly achieving victories such as at Circesium in 257, but suffered defeat near Edessa in late spring 260, resulting in his capture.

Shapur then invaded Cappadocia and Cilicia, seizing Antioch and Caesarea, though evidence for penetration into central northern Syria is lacking; his main offensive appears directed westward toward Cilicia.

Odaenathus' Campaigns

In 260 CE, after Shapur I captured the Roman emperor Valerian, Odaenathus sent a diplomatic mission to the Persian ruler with gifts carried by a large camel caravan. Arrogant from his victory, Shapur was insulted by what he saw as a lack of proper respect and had the gifts thrown into the Euphrates. Learning of this, Odaenathus swiftly raised his forces and launched a surprise attack that inflicted a catastrophic defeat on the Sasanians, though some historians question whether this story has been exaggerated.

Operating from the start as a general under Gallienus, commanding both Roman legions and his own troops, Odaenathus immediately began reclaiming Roman territory lost when Shapur had advanced west from Mesopotamia. His army—light foot archers, heavy cataphracts, lancers, and irregular Arabian cavalry—was highly effective at harassing the Persian retreat. He defeated Shapur personally and chased the fleeing Sasanians all the way to Ctesiphon, forcing them to abandon most of their Roman loot and capturing royal family members, including the king’s concubines, along with substantial booty.

After this, Odaenathus turned on eastern usurpers, besieging Quietus at Emesa, where locals killed the pretender. In reward, Gallienus appointed him dux, Corrector Totius Orientis, Dux Romanorum, and Imperator—effectively Marshal of the East—giving him broad military and civil authority over Syria and nearby regions, including the power to command governors in Syria and Mesopotamia.

Consequences

During the consolidation of imperial power in the East, Odaenathus laid the foundations for an independent kingdom in Palmyra from Rome. After his assassination in 267, his widow Zenobia brought this project to fruition, occupying Roman Egypt and part of Asia Minor. Emperor Aurelian in 272 reconquered the lost territories in the East, where the Kingdom of Palmyra had replaced the Roman Empire to counter Sasanian power.