The Roman–Parthian War of 58–63 or the War of the Armenian Succession was fought between the Roman Empire and the Parthian Empire over control of Armenia, an important buffer state between the two realms. Armenia had been a Roman client state since the days of Emperor Augustus, but in 52/53, the Parthians succeeded in installing their own candidate, Tiridates, on the Armenian throne.
These events coincided with the accession of Nero to the imperial throne in Rome, and the young emperor decided to react vigorously. The war, which was the only major foreign campaign of his reign, began with rapid success for the Roman forces, led by the able general Gnaeus Domitius Corbulo. They overcame the forces loyal to Tiridates, installed their own candidate, Tigranes VI, on the Armenian throne, and left the country. The Romans were aided by the fact that the Parthian king Vologases was embroiled in the suppression of a series of revolts in his own country. As soon as these had been dealt with, however, the Parthians turned their attention to Armenia, and after a couple of years of inconclusive campaigning, inflicted a heavy defeat on the Romans in the Battle of Rhandeia.
The conflict ended soon after, in an effective stalemate and a formal compromise: a Parthian prince of the Arsacid line would henceforth sit on the Armenian throne, but his nomination had to be approved by the Roman emperor. This conflict was the first direct confrontation between Parthia and the Romans since Crassus' disastrous expedition and Mark Antony's campaigns a century earlier, and would be the first of a long series of wars between Rome and Iranian Empires over Armenia (see Roman–Persian Wars).
Background
Ever since the expanding Roman Republic and the Parthian Empire had come into contact in the mid-1st century BC, there had been friction between the two great powers of the Near East over the control of the various states lying between them. The largest and most important of these was the Kingdom of Armenia. In 20 BC, Augustus succeeded in establishing a Roman protectorate over the country, when Tigranes III was enthroned as king of Armenia. Roman influence was secured through a series of Roman-sponsored kings until 37 AD, when a Parthian-supported candidate, Orodes, assumed the throne. The Roman-supported king, Mithridates, recovered his throne with the support of Emperor Claudius in 42 AD, but was deposed in 51 AD by his nephew Rhadamistus of Iberia. His rule quickly became unpopular, however, and this gave the newly crowned king Vologases I of Parthia the opportunity to intervene. His forces quickly seized the two capitals of Armenia, Artaxata and Tigranocerta, and put his younger brother Tiridates on the throne. The onset of a bitter winter and the outbreak of an epidemic forced the Parthian forces to withdraw, allowing Rhadamistus to retake control of the country. His behavior towards his subjects, however, was even worse than before, and they rose in rebellion against him. Thus, in 54 AD Rhadamistus fled to his father's court in Iberia, and Tiridates re-established himself in Armenia.
In the same year, in Rome, Emperor Claudius died and was succeeded by his stepson Nero. The Parthian encroachment in an area regarded as lying within the Roman sphere of influence worried the Roman leadership, and was widely seen as a major test of the new emperor's ability. Nero reacted vigorously, appointing Gnaeus Domitius Corbulo, a general who had distinguished himself in Germania and now served as governor of Asia, to supreme command in the East.
Diplomatic maneuvers and preparations
Corbulo was given control over two provinces, Cappadocia and Galatia (modern-day central Turkey), with propraetorial and later proconsular authority or imperium. Although Galatia was considered a good recruiting-ground and Cappadocia had a few units of auxiliaries, the bulk of his army came from Syria, where half the garrison of four legions and several units of auxiliaries was transferred to his command.
Initially, the Romans hoped to resolve the situation by diplomatic means: Corbulo and Ummidius Quadratus, the governor of Syria, both sent embassies to Vologases, proposing that he give up hostages, as was customary during negotiations, to ensure good faith. Vologases, himself preoccupied by the revolt of his son Vardanes which forced him to withdraw his troops from Armenia, readily complied. A period of inactivity ensued, while the Armenian issue remained in limbo. Corbulo used this lull to restore his troops' discipline and combat readiness, which had diminished in the peaceful garrisons of the East. According to Tacitus, Corbulo discharged all who were old or in ill health, kept the entire army under canvas in the harsh winters of the Anatolian plateau to acclimatize them to the snows of Armenia, and enforced a strict discipline, punishing deserters by death. At the same time, however, he took care to be constantly present amongst his men, sharing their hardships.
In the meantime, Tiridates, backed by his brother, refused to go to Rome, and even engaged in operations against those Armenians whom he deemed were loyal to Rome. Tension mounted and finally, in the early spring of 58, war broke out.
Outbreak of the war — The Roman offensive
Corbulo had placed a large number of his auxiliaries in a line of forts near the Armenian frontier under a former primus pilus, Paccius Orfitus. Disobeying Corbulo's orders, he used some newly arrived auxiliary cavalry alae to stage a raid against the Armenians, who appeared to be unprepared. In the event, his raid failed, and the retreating troops even spread their panic amongst the garrisons of the other forts. It was an inauspicious start for a campaign, and Corbulo severely punished the survivors and their commanders.
Having drilled his army for two years, Corbulo, despite this misadventure, was ready. He had three legions at his disposal (III Gallica and VI Ferrata from Syria and IV Scythica), to which were added a large number of auxiliaries and allied contingents from Eastern client kings like Aristobulus of Lesser Armenia and Polemon II of Pontus. The situation was furthermore favorable to the Romans: Vologases faced a serious revolt by the Hyrcanians in the region of the Caspian Sea as well as incursions of Dahae and Sacae nomads from Central Asia, and was unable to support his brother.
The war thus far had featured mostly skirmishing along the Roman–Armenian border. Corbulo tried to protect the pro-Roman Armenian settlements from attack, and simultaneously retaliated against the Parthians' supporters. Given that Tiridates avoided confrontation in a pitched battle, Corbulo divided his force, so that they could attack several places simultaneously, and instructed his allies, Kings Antiochus IV of Commagene and Pharasmanes I of Iberia, to raid Armenia from their own territories. In addition, an alliance was concluded with the Moschoi, a tribe living in northwestern Armenia.
Tiridates reacted by sending envoys to ask why he was under attack, since hostages had been given. To this, Corbulo reiterated the demand to seek the recognition of his crown from Nero. Eventually, the two sides agreed on a meeting. Tiridates announced that he would bring 1,000 men to the meeting, implying that Corbulo should bring the same number of men "in peaceful fashion, without breastplates and helmets". Tacitus suggests that Tiridates intended to overwhelm the Romans, as the Parthian cavalry would be superior to an equal number of Roman infantry in any case. At any rate, in a show of force, Corbulo decided to take with him the larger part of his force, not only IV Ferrata, but also 3,000 men from III Gallica plus the auxiliaries. Tiridates also appeared at the agreed site, but, seeing the Romans in full battle array, and in turn distrusting their intentions, he did not come closer and withdrew during the night. Tiridates then resorted to a tactic that had worked well a century earlier against Mark Antony: he sent forces to raid the Roman army's supply route, which stretched over the mountains back to Trapezus in the Black Sea. They failed, however, since the Romans had taken care to secure the mountain routes by a series of forts.
Fall of Artaxata
Corbulo now resolved to directly attack Tiridates' fortified strongholds. Not only were they instrumental in controlling the surrounding country and sources of revenue and soldiers, but in addition, a threat to them might force Tiridates to risk a pitched battle, since, in the words of historian A. Goldsworthy, "a king who could not defend communities loyal to him [...] lost prestige." Corbulo and his subordinates successfully stormed three of these forts, including Volandum (possibly modern Iğdır), "the strongest of all in that province" according to Tacitus, within a day with minimal casualties, and massacred their garrisons. Terrified by this display of Roman might, several towns and villages surrendered, and the Romans prepared to move against the northern Armenian capital, Artaxata.
This forced Tiridates to confront the Romans with his army, as they approached Artaxata. The Roman force, reinforced by a vexillatio of X Fretensis, marched in a hollow square, with the legions supported by auxiliary horsemen and foot archers. The Roman soldiers were under strict orders not to break formation, and despite repeated probing attacks and feigned retreats by the Parthian horse archers, they held together until nightfall. During the night, Tiridates withdrew his army, abandoning his capital; its inhabitants promptly surrendered and were allowed to leave unmolested, but the city was torched, since the Romans could not spare sufficient men for garrisoning it.
Fall of Tigranocerta
In 59, the Romans marched to the south, towards Tigranocerta, Armenia's second capital city. On their way, Corbulo's men punished those who withstood or hid from them, while leniency was shown to those who surrendered. In the harsh, dry terrain of northern Mesopotamia, the army suffered from lack of provisions, especially water, until they reached the more fertile areas near Tigranocerta. During that time, a plot to murder Corbulo was uncovered and suppressed. Several Armenian nobles who had joined the Roman camp were implicated and executed. According to a story provided by Frontinus, when the Roman army arrived at Tigranocerta, they launched the severed head of one of the conspirators into the city. By chance, it landed right where the city council was assembled; they immediately decided to surrender the city, which was consequently spared. Shortly after, an attempt by the Parthian army under king Vologases to enter Armenia was blocked by Verulanus Severus, the commander of the auxiliaries.
The Romans were now in control of Armenia, and they promptly installed its new king, Tigranes VI, the last descendant of the Cappadocian royal house, in Tigranocerta. Some outlying western parts of Armenia were also ceded to the Roman vassals. Corbulo left 1,000 legionaries, three auxiliary cohorts and two cavalry alae (ca. 3-4,000 men) behind to support the new monarch, and retired with the rest of his army to Syria, the governorship of which he now (in 60 AD) assumed as a reward for his success.
Parthian counterattack
The Romans were well aware that their victory was still fragile, and that as soon as the Parthian king had dealt with the Hyrcanian rebellion, he would turn his attention to Armenia. Despite Vologases' reluctance to risk an all-out conflict with Rome, in the end, he was forced to act when Tigranes raided the Parthian province of Adiabene in 61. The enraged protests of its governor Monobazus, and his pleas for protection, could not be ignored by Vologases, whose prestige and royal authority were at stake. Vologases therefore hastily concluded a treaty with the Hyrcanians so as to be free to campaign against Rome, and called an assembly of the grandees of his realm. There he publicly reaffirmed Tiridates' position as king of Armenia by crowning him with a diadem. In order to reinstall his brother on the Armenian throne, the Parthian king assembled a force of picked cavalry under Monaeses, complemented by infantry from Adiabene.
In response, Corbulo sent the legions IV Scythica and XII Fulminata to Armenia, while he detailed the three other legions under his command (III Gallica, VI Ferrata and XV Apollinaris) to fortify the line of the river Euphrates, fearing that the Parthians might invade Syria. At the same time, he petitioned Nero to appoint a separate legate for Cappadocia, with the responsibility for conducting the war in Armenia.