1. The Parthian offensive and the Roman mobilisation

Following a long period of peace on the eastern borders of the Roman Empire, things changed dramatically in 161 AD. In the spring, shortly after Marcus Aurelius and Lucius Verus were proclaimed co-emperors, the Parthian king Vologeses IV¹ launched an attack he had been planning for a long time, thus causing yet another war between Rome and Parthia.² Although the information from the surviving ancient sources is scarce and fragmentary, combined with certain archaeological evidence they allow the reconstruction of the events in broad terms.

The army of Vologases invaded Armenia and the Parthian prince Pacorus was proclaimed king. The governor of Cappadocia, Marcus Sedatius Severianus (of Celtic descent), led a legion into Armenia to face the invaders, but he was trapped at Elegeia (possibly modern Iliga) by the forces of general Osroes. Within three days the Roman army was almost completely annihilated and Severianus committed suicide.³ The war front became widened when another Parthian army stroke at Osroene and captured Edessa (modern Urfa). The pro-Roman king Mannus was deposed and another man bearing the Syrian name Wael was installed at his place, known only through his coinage.⁴ Following these successes, the Parthians crossed the Euphrates and marched into Syria. The Roman governor, Lucius Attidius Cornelianus, attempted to intercept them, but was defeated and forced to retreat.⁵ The situation was now extremely dire, as the population of Syria seemed to harbour revolutionary feelings.⁶

At Rome it was decided that Lucius Verus should conduct this campaign personally; he sailed off from Italy in 162 AD. After making stops at Corinth, Athens, Chios and Ephesus he continued into Lycia, Pamphylia and Cilicia, always travelling by boat. His whole voyage towards Syria appears to have been rather slow and was accompanied by luxurious festivities.⁷ Late in 162 or early in 163 AD he reached Antioch (modern Antakya) where he set up his headquarters for the following years.⁸ During his stay at Syria it seems that Verus was not particularly zealous with respect to his military duties, entrusting the command of the operations to his experienced generals. During the summers he resided at Daphne, a suburb of Antioch, while he overwintered at the coastal city of Laodicea (modern Lattakia); the rest of the year he spent in Antioch were he busied himself mostly with keeping himself entertained with various spectacles and hunting.⁹ His conduct and lifestyle were derided by the locals.¹⁰ Following the insistence of his generals he made a single visit to the front lines at Euphrates in 163 AD, only to rush back to Ephesus in order to greet his future wife, the sister of Marcus Aurelius.¹¹

In the meantime, there was great mobilisation of forces in the threatened areas. Three legions arrived from Europe: I Minervia, ΙΙ Adiutrix and V Macedonica. It is also possible that contingents of or the entire legions I Adiutrix , ΙΙ Traiana, ΙII Augusta, ΙΙΙ Gallica and Χ Gemina also participated in the campaign.¹² Finally, there is a reference pertaining to the participation of a Celtic and a Mauritanian contingent.¹³ Due to the relative neglect of the army during the previous peaceful period and the recent defeats of the Romans, the legions were in a poor condition in terms of fighting ability, discipline, armament and morale. Thus, the military command took a series of measures to improve their state before attempting to launch them into battle.¹⁴

2. The Roman counteroffensive

Originally Verus made diplomatic overtures, but his peace proposals were rejected by Vologases.¹⁵ The first objective of the Roman counterattack was Armenia, which was invaded in 163 AD by the new governor of Cappadocia, Marcus Statius Priscus.¹⁶ By the end of the year, he had managed to drive out the Parthians and king Pacorus and had captured the capital, Artaxata. Furthermore, he entrenched Roman rule in the region by founding a new capital, Caenopolis, where he immediately installed a Roman garrison which remained there for several years. Following this success, Verus acquired the title Armeniacus (Armenian) and in 164 AD he installed Soaemus on the throne of Armenia, a Roman senator of Parthian descent.¹⁷ A notable consequence of the Armenian campaign, was Bithynia's convertion from a senatorial to an imperial province, possibly in 164/5 AD, on account of the strategic importance it acquired under the particular historical circumstances, as it was there that all the roads leading to Armenia (through Paphlagonia and Galatia) begun. Because of the need to transport troops from Europe to Asia and obviously due to the decision to maintain tighter control over Armenia, as recently exhibited by Priscus and Verus, it was deemed necessary to make Bithynia an imperial province.¹⁸

For the campaigns that followed in Syria and Mesopotamia, the scarcity of the available evidence renders impossible any attempt to present a clear picture of the operations and their precise dates. Thus, a number of theories have been put forward concerning the unfolding of the war.¹⁹ Possibly in 163 AD a Roman army under the command of Avidius Cassius gradually pushed the Parthians out of Syria and in the following year moved south along the Euphrates where it joined battle with the enemy at Soura. Then it crossed the river and it captured Dausara and Nicephorium (modern Rakka). In 165 AD Cassius marched again towards the south, defeated the Parthians in a great battle close to Doura-Europus and captured the city; during this period possibly some of the vassal rulers of Vologases begun abandoning their common struggle. We then have some sort of a pact or truce and Cassius arrived peacefully at Seleuceia, which still contained a great number of Greeks.

However, in December of 165 AD the Romans sacked and burned part of the city alleging that the agreement had been breeched by the inhabitants of Seleuceia. The Parthian capital of Ctesiphon suffered the same fate, where Vologases’ palace was destroyed. At Seleuceia some soldiers were infected by an up to then unknown to the western world disease, possibly smallpox. Soon the deadly epidemic spread and forced the Romans to retreat to Syria, leaving a great number of dead behind. Later, as the soldiers who participated in the Parthian War returned, the epidemic spread in Asia Minor and Europe with catastrophic results.²⁰

It is unclear when exactly the Romans captured Osroene and restored Mannus to the throne of Edessa. The capture of Nisibis (modern Nusayabin), where the epidemic had broken out, occurred probably early in 166 AD. The only thing certain is that the Roman advance continued to the east, beyond the Tigris, and came to a halt in the Spring of 166 AD, when an army under Cassius infiltrated into Media.²¹ Following his victories in Mesopotamia during the previous year Verus had taken on the epithet Parthicus Maximus, while his last successes allowed him to also take on the title Medicus.²² Apparently Vologases was in a very difficult position and was forced to sign a treaty, on the terms of which nothing whatsoever is known. Indubitably the epidemic affected the decision of the warring sides to cease hostilities.

Following the end of the war, Martius Verus was appointed governor of Cappadocia, up to then he had been commander of Legio V Macedonica, and had distinguished himself mainly during the operations in Armenia.²³ After resolving various other administrative matters, the emperor reluctantly left Syria for Rome early in the summer; crossing Asia Minor he reached Ephesus where he was greeted with celebrations and later an imposing monument was erected to commemorate his victory.²⁴ For 13 months the troops that returned to Europe passed through Ephesus, and their upkeep was undertaken by the local official and sophist Flavius Damianus.²⁵ After the arrival of Verus at Rome late in the summer of 166 AD a triumph was held.²⁶

Vologases’ defeat was another indication of the temporary decline of Parthia’s strength and the downfall of the Arsacid dynasty. The tangible territorial gains for Rome where not so extensive. Rome’s borders were expanded to east of the Euphrates and were now defined by the line created by Europus, the river Chaboras (modern Khabur) and the mountain nowadays called Jabal Sinjar. In the next thirty years peace reigned between the two states notwithstanding certain temporary moments of tension.²⁷