Chapter Twenty-Three: The Reigns of Vologases IV, Vologases V, and Artabanus IV

Introduction: The Context of Late Parthian Rule

The late second and early third centuries CE marked the final, fateful decades of the Arsacid dynasty’s struggle to preserve its sovereignty against Roman imperial expansion. By this time, Parthian Iran and Rome had been rivals for nearly three centuries, their conflict expressed in a recurring pattern of border wars, client-kingdom diplomacy, and intermittent truces. Yet the challenges of this period went far beyond military rivalry. Both powers faced internal vulnerabilities: political instability, economic strain, and the shock of a global pandemic whose impact reached far beyond demographic loss.

For Vologases IV (r. 147–191 CE) and later Artabanus IV (r. 213–224 CE), foreign policy was inseparable from the management of a diverse, decentralized empire. The Arsacid state was held together by a complex mosaic of satrapies, semi-autonomous client kingdoms, and tribal aristocracies, all of which required careful balancing. Maintaining this cohesion depended heavily on the Silk Road and maritime trade through the Persian Gulf, the lifeblood of Parthia’s economy. Any disruption to these routes—whether by Roman campaigns, nomadic incursions, or plague—threatened the empire’s stability at its core.

This chapter begins with two intertwined developments that would shape the late Arsacid era: the Antonine Plague and its cascading economic, military, and cultural consequences; and the smooth succession from Vologases IV to Vologases V at precisely the moment Rome was thrown into one of the most chaotic episodes in its history.

I. The Antonine Plague and Its Geopolitical Consequences (165–180 CE)

I.i. Origins and Spread of the Pandemic

The Antonine Plague, named after the Roman imperial family of Marcus Aurelius, is believed to have first erupted during the Roman siege of Seleucia in the winter of 165–166 CE. Seleucia—once the seat of the Seleucid Empire—remained one of the greatest cities of Mesopotamia under Parthian rule, paired with nearby Ctesiphon as a political and commercial hub of Iran.

Ancient sources, including Galen’s medical observations, describe symptoms consistent with smallpox, though the exact disease remains uncertain. What is clear is that Roman troops returning from Mesopotamia carried the contagion along the imperial road system, igniting an epidemic that spread from Syria to Gaul and from Egypt to the Danube.

The mortality was catastrophic. Modern demographic models estimate that up to one-third of the population in some Roman provinces perished, amounting to perhaps five to seven million dead across the empire. Although contemporary Parthian records are sparse, the disease almost certainly ravaged Mesopotamian cities, caravan stations, and the agricultural heartlands of Babylonia and Media, where dense populations and constant movement of merchants made containment impossible.

I.ii. Strategic Impact on Roman–Iranian Relations

The pandemic’s first strategic consequence was the blunting of Roman offensive capability. At the moment when Lucius Verus and Marcus Aurelius had completed a successful eastern campaign, the loss of soldiers and auxiliary manpower undermined their ability to consolidate gains in Mesopotamia. Garrison numbers dwindled, recruitment became urgent but less selective, and Rome’s military attention soon shifted to crises along the Danube.

For Iran, the plague offered an unexpected breathing space. Vologases IV was able to reinforce the Euphrates line, rebuild fortifications in northern Mesopotamia, and strengthen ties with loyal vassals such as Osroene and Adiabene. In the Caucasus, Arsacid diplomacy secured a network of client rulers in Armenia, Iberia, and Albania, creating a defensive arc against both Roman encroachment and nomadic pressures from the north.

Yet the economic cost was heavy. The Silk Road routes from Central Asia slowed dramatically as caravan cities like Merv, Hecatompylos, and Hatra suffered outbreaks. The maritime link through Charax Spasinu, the great port at the head of the Persian Gulf, saw a decline in customs revenues as Indian Ocean traders curtailed voyages. These losses forced the Parthian court to seek alternative revenue sources, including increased taxation on Mesopotamian estates—a policy that risked alienating the powerful landed aristocracy.

I.iii. Social and Religious Ramifications

In Rome, the Antonine Plague altered cultural perceptions as much as it weakened the state. Christian communities gained visibility and moral authority by tending to the sick and burying the dead, often in stark contrast to the flight of pagan elites from infected areas. This reputation for compassion accelerated Christian conversions in urban centers—an effect not confined to Roman territories.

In Iranian lands, particularly in Syriac-speaking Mesopotamia, Christianity’s early growth coincided with the pandemic years. Cities such as Edessa, Nisibis, and Arbela became centers of Christian learning and worship. Although still minor in numbers, these communities benefited from the Arsacid Mithraic tradition of religious pluralism—a policy rooted in the need to govern an empire containing Zoroastrians, Jews, Hellenized pagans, and a multitude of local cults.

The trans-Euphrates Christian networks that began forming during this period would, in the centuries to come, link Mesopotamian churches to Antioch in the west and to Iran and Central Asia in the east—bridging the cultural space between the two rival empires in a way neither Rome nor Parthia had anticipated.

II. The Succession of Vologases V and the Roman Imperial Crisis (191 CE)

II.i. A Peaceful Parthian Transition

The death of Vologases IV in 191 CE—uncannily simultaneous with the assassination of Commodus in Rome—offered a striking contrast between the political cultures of the two empires. In Iran , succession was orderly and uncontested. The Parthian Senate, composed of leading noble houses and regional satraps, confirmed the ascension of Vologases V, son of Sanatruk, King of Armenia.

As King of Armenia, Vologases V had demonstrated a rare blend of diplomacy and firmness, preserving Arsacid control in a region long contested by Rome. He also secured the Iberian throne for his son Rev, establishing a family-based alliance network across the Caucasus.

II.ii. An Unprecedented Dynastic Arrangement

Upon becoming King of Kings, Vologases V undertook a dynastic strategy unprecedented in Arsacid history: he placed another son, Khosrow I, on the Armenian throne, while Rev continued to rule Iberia. This double satellite kingship gave Parthia unprecedented leverage in the northern frontier zone. It ensured that two of the most strategically vital buffer kingdoms were ruled by immediate family members loyal to Ctesiphon, securing both trade routes through the Caucasus and the approaches to the Caspian Gates.

II.iii. Roman Imperial Chaos and the Rise of Septimius Severus

While the Parthian transition strengthened dynastic cohesion, Rome descended into the Year of the Five Emperors. Commodus’s assassination was followed by the brief reign of Pertinax, murdered by the Praetorian Guard; the infamous auctioning of the empire to Didius Julianus; and the rebellions of Pescennius Niger in Syria and Clodius Albinus in Britain.

Into this maelstrom marched Septimius Severus, governor of Upper Pannonia, whose legions from the Danube front gave him the decisive advantage. Severus’s victory marked the triumph of the military dictatorship, in which the loyalty of the legions outweighed senatorial legitimacy or hereditary claim.

From the Iranian perspective, this shift in Roman politics carried an ominous implication: emperors who owed their power to soldiers would often seek military glory abroad to maintain their authority at home. In Severus, the Arsacids faced a ruler for whom an eastern war was not merely a strategic option but a potential political necessity—foreshadowing the renewed confrontation that would come within two decades.

III. The Niger Rebellion and Parthian Diplomatic Calculations (193–194 CE)

III.i. An Eastern Challenge to Severus

The consolidation of Septimius Severus’s authority was far from immediate. In both the eastern and western provinces of Rome, powerful governors with loyal legions challenged his legitimacy. In the West, Decimus Clodius Albinus, governor of Britain, initially accepted a pact with Severus but later broke with him. In the East, the far more immediate and destabilizing threat came from Gaius Pescennius Niger, the influential governor of Syria, who openly defied Severus’s claim to the purple.

Niger’s rebellion disrupted the delicate balance of power in the Roman East and posed a particular problem for the economic lifeline of the Mediterranean–Asian trade system. Syria and Palestine were crucial transit zones for luxury goods from India and China, much of which passed through Iran's Parthian-controlled routes before reaching Roman markets. The unrest jeopardized customs revenues, reduced caravan security, and created opportunities for Iran to exert leverage over the regional flow of commerce.

III.ii. Vologases V’s Diplomatic Miscalculation

In 193 CE, Niger’s forces proclaimed him emperor at Antioch, rallying support from Palestine, Egypt, and Bithynia. Sensing an opening to influence Roman succession in his favor, Vologases V appears to have entered into negotiations with Niger. Ancient sources suggest that Vologases may have believed the Roman Senate would confirm Niger as emperor, and that his intervention might align with the lawful choice of Rome’s traditional political authority.

This was a critical miscalculation. While Vologases waited for news from the Senate, Severus had already been proclaimed emperor by the Pannonian legions and quickly secured senatorial recognition. The window for effective Parthian diplomatic influence closed rapidly, leaving Vologases in the unenviable position of having appeared to support the losing side.

III.iii. Regional Alliance Responses

Niger, desperate for allies, dispatched envoys to three key regional rulers: Vologases V of Parthia, Khosrow I of Armenia (Vologases’s son), and Barsemius of Hatra. Herodian records the differing responses:

“The king of Armenia replied that he would make no alliance with anyone, and that he was ready to defend his country even if Severus attacked him. The king of Parthia, on the other hand, said that he would order his governors to raise an army – and this was their usual reaction when they needed an army, since they had no standing army and did not employ mercenaries. But Barsemius, king of the Hatarai, sent his native archers to Niger’s aid.”

While Armenia maintained strict neutrality, Barsemius’s decision to send troops almost certainly reflected Iranian suzerainty over Hatra. The city was a key federate state guarding desert caravan rutes between the Tigris and the Levant. Its support for Niger was therefore very likely coordinated—at least tacitly—by Vologases V as part of a limited, deniable intervention in Roman affairs.

This episode underscores a recurring Arsacid strategy: indirect engagement through client states rather than direct confrontation, allowing Iran to probe Roman vulnerabilities without committing the royal Parthian field army or openly declaring war.

IV. Severus’s Eastern Campaigns and Parthian Resistance (194–199 CE)

IV.i. Roman Opportunism and Initial Success

The instability in Rome’s eastern provinces briefly created a strategic opportunity for Iran. Encouraged by Niger’s rebellion, Roman client states in Asia Minor and northern Mesopotamia rose in revolt against Severus. Parthian forces, supported by Arab auxiliaries from Adiabene and Osroene, launched coordinated attacks on Roman positions, systematically eliminating garrisons and laying siege to Nisibis, the principal Roman military stronghold east of the Euphrates.

When Severus personally arrived at Nisibis, he broke the siege and reasserted control. Mesopotamian envoys then approached his camp, claiming their rebellion had been directed solely against Niger and offering to depart peacefully. Severus, however, saw in this unrest an opening for conquest. Disregarding the logistical and financial strain of campaigning deep into Iranian territory—challenges that had undone his predecessors—he prepared for an aggressive advance.

IV.ii. The Limits of Roman Ambition

Severus’s strategic objective went beyond punitive action. He aimed to annex at least three key Parthian Iran's federate states—Adiabene, Osroene, and Hatra—which had long been coveted by Rome for their strategic position along caravan routes and their role as buffer states.

Yet Vologases V responded with a time-tested Arsacid tactic: strategic withdrawal. Parthian forces fell back into the Iranian interior, avoiding direct pitched battles while disrupting Roman supply lines. Without a decisive engagement, Severus’s extended lines became vulnerable to attrition, forcing him to reconsider the scope of his offensive.

IV.iii. The Sack of Ctesiphon and Strategic Failure

In 198 CE, Severus achieved what at first glance seemed a spectacular victory: the capture of Ctesiphon, the Parthian capital. But unlike Avidius Cassius, who had treated the city’s inhabitants with clemency decades earlier, Severus vented his frustrations at the lack of provisions and the toll of disease by ordering massacres, ethnic cleansing, and mass enslavement. Thousands were deported westward, further depopulating an already plague-weakened Mesopotamia.

Despite the sack, this was a pyrrhic victory. The Romans lacked the resources to hold the city or its surrounding territory. Cassius Dio records that famine and disease ravaged the army—soldiers were reduced to “living on the roots of plants” and suffered “various diseases and ailments.” Severus was compelled to withdraw, his campaign yielding no lasting territorial gain and alienating the very populations whose cooperation would have been essential for Roman control.

IV.iv. The Failure at Hatra

The final humiliation came at Hatra, a federate city renowned for its formidable fortifications and mastery of desert warfare. Severus laid siege for twenty days, but Herodian describes how the defenders rained down stones, “scorpions” (torsion siege bolts), and earthenware vessels filled with venomous insects upon the besiegers. The Roman troops, unaccustomed to the intense desert heat, suffered heatstroke, disorientation, and high mortality.

Even at the height of Roman imperial power, Hatra withstood every assault, demonstrating the resilience of Iran’s network of client fortresses. Severus’s failure there mirrored the frustrations of Trajan and Avidius Cassius before him, underscoring the enduring limits of Roman penetration into the Mesopotamian–Arabian frontier zone.

The twin episodes of Ctesiphon and Hatra illustrate a broader truth about late Parthian Iran warfare: even when Rome could achieve dramatic battlefield successes, the combination of Iranian strategic depth, client-state loyalty, and the environmental challenges of the East prevented the consolidation of lasting gains.

V. Vologases V’s Strategic Restraint and the Question of Succession

V.i. A Policy of Calculated Restraint

The historian George Rawlinson, in his 19th-century survey of Parthian history, criticized Vologases V for failing to exploit Rome’s vulnerability during the years of Severan civil wars and military overextension. From a purely opportunistic military standpoint, it might seem that a large-scale counter-offensive could have yielded territorial gains or reversed the humiliation of Ctesiphon’s sack.

However, such criticism overlooks the strategic calculus of late Arsacid kingship. The Parthian monarchy was not a centralized autocracy in the Roman mold but a confederated system in which the King of Kings balanced the competing interests of powerful noble houses, semi-autonomous satrapies, and client monarchies. Mobilizing for a full-scale invasion would have required unprecedented consensus among these stakeholders, risking internal cohesion.

Moreover, by the early 3rd century CE, the Parthian Iran’s prosperity rested heavily on its role as the central corridor of Eurasian commerce. The silk, spices, gems, and fine textiles flowing from the Han Chinese and Kushan Empires through Iranian territory to Roman markets were an essential revenue source—not only for the royal treasury but for the aristocratic elites who controlled caravan cities and customs stations. A protracted war risked disrupting these lucrative trade relations with the affluent empires to the east, whose markets and alliances were far more profitable in the long term than ephemeral military glory against Rome.

In this light, Vologases V’s decision to limit hostilities can be seen not as weakness, but as prudent statecraft—a policy aimed at preserving the empire’s economic lifelines while Rome expended its strength in self-inflicted turmoil.

V.ii. The Succession Question: Vologases V and Artabanus IV

Western scholarship, relying heavily on numismatic evidence, has sometimes interpreted the overlapping coinage of Vologases V and Artabanus IV as proof of a succession struggle between the two sons of Vologases IV after their father’s death. In Roman historical terms, such a scenario suggests a civil war. Yet, in the Parthian Iran context, this interpretation is far from certain.

The Arsacid system permitted provincial governors and client kings to mint coins bearing their own likenesses and titles—often as a mark of local authority within the broader imperial framework. Coinage, therefore, does not necessarily imply claims to universal sovereignty. The absence of any reference to such a conflict in Iranian or Armenian historical traditions suggests that if a dispute occurred, it was localized and short-lived, rather than a full-scale civil war.

A more plausible reconstruction is that Vologases V exercised authority primarily as a federate king ruling from Ctesiphon for roughly eight years, while Artabanus IV—whose reign is traditionally dated 213–224 CE—held the higher title of Shahanshah (“King of Kings”) and directed overall imperial policy from eastern Iran. This arrangement, far from being anomalous, fits the flexible and often polycentric governance model of the Arsacid state.

VI. Caracalla’s Reign of Terror and Eastern Ambitions (211–217 CE)

VI.i. Fraternal Murder and Imperial Madness

Ironically, the sort of destructive dynastic conflict Roman historians accused the Parthians of harboring was unfolding in Rome itself after the death of Septimius Severus in 211 CE. Severus had attempted to secure a stable dual monarchy by naming his two sons, Caracalla and Geta, as co-emperors, counseling them to “live in harmony, enrich the soldiers, and disregard everyone else.”

But the brothers’ mutual hatred was too deep. Barely a year into their joint reign, Caracalla arranged for Geta’s assassination in the presence of their mother, Julia Domna. Ancient biographer Aelius Spartianus painted a damning portrait of Caracalla as “the most cruel of men, and all in one word, fratricide, slanderer of relatives, enemy of father, mother, and brother.” The murder unleashed a wave of purges: thousands of Geta’s supporters—senators, equestrians, soldiers, and even women—were executed, their property confiscated.

This internal bloodletting not only destabilized the Roman political elite but also projected weakness to foreign powers, including Iran, where news of fratricide and mass executions would have reinforced perceptions of Rome’s political volatility.

VI.ii. The Alexander Complex

Caracalla’s reign (211–217 CE) was defined as much by psychological excess as by political cruelty. Obsessed with Alexander the Great, he consciously styled himself as the Macedonian conqueror reborn—wearing Macedonian dress, commissioning Alexandrian iconography on coins, and making pilgrimages to Alexander’s tomb in Alexandria.

This fixation was more than vanity; it shaped his foreign policy. Convinced that true imperial greatness required eastern conquests to match Alexander’s, Caracalla turned his gaze to Parthian Iran and Armenia . In doing so, he embraced a militarized vision of tyranny in which legitimacy was to be secured through the spectacular humiliation of long-standing rivals.

Domestically, governance languished. Real administrative power often lay with Julia Domna, while Caracalla indulged in chariot racing, gladiatorial games, and displays of martial theater. The neglect of civic administration for personal militaristic ambition foreshadowed his reckless approach to diplomacy in the East.

VI.iii. Treacherous Diplomacy in the East

In the summer of 215 CE, Caracalla traveled to Antioch, positioning himself for an eastern campaign under the guise of diplomatic outreach. He summoned Abgar IX, king of Osroene—a semi-independent Arab kingdom under Iranian suzerainty—to a “friendly” meeting. There, he arrested Abgar, imprisoned him, and declared Osroene a Roman province.

Emboldened by this deception, Caracalla repeated the tactic with Khosrow I of Armenia (son of Vologases V). Yet this time, the gambit backfired. Upon learning of their king’s capture, the Armenians launched a fierce rebellion, defeating the Roman forces under General Theocritus and inflicting heavy casualties. The resistance demonstrated both the resilience of Armenia’s martial traditions and the limits of Roman military power in the rugged and fiercely independent highlands.

Caracalla’s duplicity destabilized the delicate balance of influence in the northern frontier. Instead of weakening Parthian Iran power, it galvanized anti-Roman sentiment among the federate kingdoms and exposed the fragility of Rome’s hold over the contested borderlands.

VII. The Marriage Proposal Deception (216 CE)

VII.i. Caracalla’s Elaborate Stratagem

By 216 AD, Caracalla had come to recognize that the Parthians' military strength made a decisive Roman victory over Iran unlikely. The failure of his Armenian campaign had already demonstrated the perils of underestimating local resistance, and a direct assault risked dragging Rome into yet another protracted and costly war. Instead, he conceived a plan of remarkable duplicity—one so damaging to Roman dignity that later historians frequently softened or erased its more shameful details.

According to Herodian’s detailed account, Caracalla dispatched a letter to Artabanus IV proposing marriage to the Parthian king-of-king’s daughter. In his message, Caracalla argued for a dynastic union of the two greatest empires on earth:

“Parthia and Rome were the greatest empires in the world; and if they were united by this marriage, an empire without a rival would be born, which would no longer be divided by a river… the Roman infantry was invincible in close combat with the spear, and the Parthians had a large force of very efficient horse archers.”

By framing the proposal as the birth of a new world order, Caracalla sought to disarm suspicion and lure Artabanus into a false sense of security.

VII.ii. Artabanus IV’s Initial Rejection and Eventual Acquiescence

Artabanus IV at first responded with characteristic Iranian pride, rejecting the idea outright:

“It is not fitting for barbarians to intermarry with the Romans. How could spouses be compatible when they did not understand each other’s language and differed so much in food and clothing?”

Yet Caracalla persisted. He inundated the Parthian court with lavish gifts, repeated professions of personal affection for the Iranian princess, and sworn oaths of goodwill toward the Arsacid realm. Gradually, the Parthian monarch relented. Addressing Caracalla as his “future son-in-law,” Artabanus agreed to the match, a gesture that would have symbolized unprecedented parity between the two empires had it been genuine.

VII.iii. The Massacre at Arbela

When the betrothal was announced, the Iranians prepared a grand welcome for the Roman emperor. Caracalla crossed the frontier unopposed, greeted with sacrifices, flower-strewn altars, and incense-filled processions. Near the royal residence at Arbela, Artabanus himself rode out to meet his guest.

Herodian paints the scene vividly:

“All the Parthians, with crowns of ceremonial flowers on their heads and robes of gold woven in various colors, were celebrating this festival… They had abandoned their horses, and laid aside their bows and quivers.”

At that moment, Caracalla gave the signal. Roman troops fell upon the unarmed Iranian celebrants, cutting them down amid the music and dancing. Artabanus barely escaped with a small guard; the festival grounds became a killing field.

VII.iv. Desecration and Withdrawal

On his return through Adiabene, Caracalla committed an act of cultural desecration unparalleled in Roman–Iranian relations: the violation of the Arsacid royal tombs. He ordered them opened, the remains of Parthian kings scattered to the wind. Even the usually pro-Roman historian Rawlinson could only condemn this as the work “of a madman, not a tyrant.”

Caracalla’s massacre destroyed any prospect of diplomatic accommodation. Artabanus now had both the moral justification and the popular mandate to pursue total retribution.

VIII. The Assassination of Caracalla and Macrinus’s Accession (217 CE)

VIII.i. Palace Intrigue and Murder

Among Caracalla’s senior commanders was Macrinus, the praetorian prefect, whom the emperor frequently humiliated in public and threatened with execution. When Caracalla wrote to his confidant Martianus to inquire about potential conspiracies, Martianus — seeking to ruin Macrinus — falsely accused him of treachery.

In a fatal misstep, Caracalla handed the sealed correspondence to Macrinus for review. Discovering his own death sentence, Macrinus began plotting. He enlisted Martialis, an officer whose brother Caracalla had executed, to carry out the act. In spring 217 CE, as the emperor traveled to the temple of Luna near Carrhae, Martialis struck while Caracalla had dismounted to relieve himself, stabbing him from behind.

VIII.ii. Macrinus’s Rise to Power

Macrinus feigned grief, convincing the soldiers that Martialis had acted out of personal revenge. With Caracalla cremated and his ashes sent to Julia Domna (who soon died—whether by suicide or at Macrinus’s order remains uncertain), the army proclaimed Macrinus emperor.

However, he inherited more than the purple; he inherited the vengeance of Artabanus IV, whose wrath had only intensified with Caracalla’s death.

IX. The Battle of Nisibis and Rome’s Humiliating Defeat (217 CE)

IX.i. Artabanus IV’s Quest for Vengeance

By mid-217 CE, Iranian forces were mobilized on an unprecedented scale. Artabanus IV marched west with a formidable Iranian host of cavalry, cataphracts, and horse archers, intent on avenging the massacre at Arbela and the desecration of his ancestors’ tombs.

Addressing his troops, Macrinus attempted to frame the coming battle as existential:

“This is not a conflict over borders or riverbeds… all depends on the challenge that we face with a formidable king who has come to fight for his children and his family.”

But the Roman army’s morale was low, and its leadership untested in the face of a fully committed Parthian offensive.

IX.ii. The Three-Day Battle

At Nisibis, the two armies clashed in a confrontation that would decide the final balance of power between Rome and the Arsacid dynasty. At dawn, the Parthians saluted the sun and Mithra, invoking divine favor before unleashing volleys of arrows.

For two days, combat raged from sunrise to sunset without a decisive breakthrough. On the third day, Artabanus altered his tactics, using his numerical superiority to stretch the Roman lines to the breaking point. Forced to extend his frontage to avoid encirclement, Macrinus weakened the depth of his formations. Parthian cavalry then punched through the thin Roman center, shattering cohesion.

The rout was total. Macrinus was among the first to flee, leaving his army leaderless.

IX.iii. The Humiliating Peace Treaty

Macrinus sued for peace, offering personal apologies for Caracalla’s treachery and pledging to restore what Rome had taken. Artabanus IV dictated terms from a position of absolute strength:

The return of all enslaved Iranian citizens.
The restoration of all plundered goods.
A massive indemnity to compensate for the destruction inflicted by Caracalla’s campaign.

Rome, for the first time in centuries of eastern conflict, agreed to a treaty that openly acknowledged Iranian military superiority.

Conclusion: The End of an Era

The Battle of Nisibis in 217 CE marked the definitive close of three centuries of intermittent Roman–Iranian warfare. In this final chapter, the Arsacid monarchy—despite its internal complexities and confederate structure—had preserved Iranian independence, inflicted a decisive battlefield defeat on Rome, and secured a peace on favorable terms.

The contrast between the two empires in these years could not be starker. Rome, riven by civil war and dominated by the personal ambitions of military emperors, stumbled from one crisis to the next. Parthian Iran, though decentralized, retained a capacity for strategic patience, flexible diplomacy, and devastating counterstrike when provoked.

Artabanus IV’s victory at Nisibis was more than a tactical success; it was a vindication of a model of imperial governance that relied on federated alliances, economic integration, and the careful husbanding of military force. Yet the triumph was bittersweet: within a decade, the Arsacid dynasty would fall to the rising Sassanid power in Persia, whose ambitions toward Rome would inaugurate a new and even more intense phase of east–west confrontation.

The legacy of Vologases IV, V, and Artabanus IV is thus twofold: they demonstrated that Rome’s expansion had limits, and they bequeathed to their Sassanid successors both the political inheritance of the Arsacid realm and the memory of a final, glorious victory over the legions of the West.

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Footnote:

The reason some historical texts refer to the last Parthian king as Artabanus IV while others call him Artabanus V is due to a long-standing debate among scholars about the correct numbering of the Arsacid kings. The confusion stems from the lack of reliable, contemporary Parthian sources and the reliance on later Greek, Roman, and Armenian accounts, which can be inconsistent.

Here's a breakdown of the key factors that contribute to this discrepancy:

Disputed Kings and Chronologies: The primary issue is the existence and numbering of some early Arsacid kings. For instance, some scholars, such as G.R.F. Assar, identify an early king named Arsaces II (r. 211–185 BC) with the name Artabanus I. This adds an extra Artabanus to the list.
The "Unnamed" Rulers: There are also proposed chronologies that include rulers whose existence is not universally accepted or whose names are not fully known. The inclusion or exclusion of these figures can shift the numbering of later kings.
Coinage and Numismatics: Scholars often rely on numismatic evidence (coins) to establish the sequence and reign dates of Parthian kings. However, interpreting these coins can be complex, and different scholars have proposed different interpretations, leading to varying chronologies. The style of the Greek legends on the coins, for example, can be used to distinguish between kings with the same name, but even this can be a subject of debate.
Older vs. Newer Scholarship: In older scholarship, the final Artabanus was often referred to as Artabanus V. However, more recent research, particularly the work of scholars who have revisited and re-evaluated the sources and numismatic evidence, has led to a widely accepted consensus that he should be numbered as Artabanus IV.