8

The Parthians, Nomadic Foes of Imperial Rome

In the failing light of June 3, 53 BC, Marcus Licinius Crassus, proconsul of Rome, realized that he had lost the battle.1 Parthian horse archers surrounded his legionaries, who had closed ranks into a defensive square to await an opportunity to charge the mounted foe when the Parthians exhausted their supply of arrows. Their chance never came. Surena, the Parthian commander, had improvised a train of camels to keep his archers supplied. The Parthians, perhaps twenty thousand strong, were significantly fewer than the Romans, but they enjoyed decisive mobility on the rolling countryside to the northeast of Carrhae (today Harran) in Mesopotamia. Crassus had erred in departing from the main road, advancing across a swollen river late in the day. Centurions and legionaries fell out for a late lunch, but then Crassus ordered them back into formation to press on. The proconsul had received reports that the enemy were nearby. The hungry, thirsty legions blundered into a favorite ruse of encirclement used by nomadic horsemen. Crassus’s cavalry was driven off in confusion, and his own son Publius fell in the retreat. The Roman legionaries doggedly stood their ground while their tormentors rained arrows on them. Toward evening, Crassus ordered a retreat to Carrhae that turned into a rout as the Romans rushed to the safety of the city. The next morning, Crassus organized a breakout in three columns. Only the column under Gaius Cassius Longinus, a future assassin of Julius Caesar, reached the bridge at Zeugma over the Euphrates, and thus safety. Crassus and the other two columns were forced to surrender. Surena ordered Crassus beheaded, and the head was sent to Ctesiphon to serve as a prop as Pentheus’s head in Euripides’s Bacchae, to the amusement of his master, the king Orodes. Out of an army of forty-five thousand, twenty thousand Romans fell in battle; another ten thousand, along with their legionary eagles, were captured. The magnitude of the Parthian victory shocked Rome. Crassus failed in logistics and reconnaissance, and so deserves the blame for the defeat. But he, like many Romans, held the Parthians in contempt as effete and cowardly barbarians. The Parthians had proved otherwise, and they changed the course of Roman history. The death of Crassus left the two surviving triumvirs, Julius Caesar and Pompey the Great, as rivals destined to clash in a civil war that destroyed the Roman Republic.

The Arsacid kings of Parthia were descendants of Iranian-speaking nomads who had dwelled immediately east of the Caspian Sea.2 Their tribe, originally called the Parni, had been members of the Scythian confederacy of the Dahae. In 247–246 BC, the princely brothers Arsaces and Tiridates seized the satrapy of Parthia from the Seleucid kings, the successors to Alexander the Great’s Asian domains. The satrapy comprised the lands between the low mountain range of the Kopet Dag and the middle Oxus valley, on the border of Iran and Turkmenistan today.3 The principal settlement, Nisa, remained the ancestral Parthian capital and royal cemetery for the next five centuries. From their new home, the princes and their followers took the new ethnic name of Parthians.

Within fifty years, four able Arsacid kings wrested from the Seleucid kings Iran and Mesopotamia, and so fell heir to the Achaemenid monarchy of Persia. In the summer of 139 BC, Mithridates I (171–138 BC) decisively defeated and captured the Seleucid king Demetrius II Nicator.4 Mithridates occupied Media, Persia, and Babylonia—the heartland of the Achaemenid Empire—and assumed the title King of Kings.5 Demetrius Nicator, ever irrepressible, soon won many friends at the Parthian court. At age fourteen, Demetrius had regained his throne from a usurper, and now the young king charmed his captors Mithridates and then his son and successor Phraates II. Demetrius was married to Rhodogune, a daughter of Mithridates, who overlooked the inconvenient condition that Demetrius was already married to a Ptolemaic wife. Twice Demetrius effected his escape in ingenious disguises; each time he was detected and returned to a gilded captivity, and his Parthian wife.6 After just over ten years of captivity, Phraates released Demetrius to incite civil war in the Seleucid Empire, because Demetrius’s brother Antiochus VII Sidetes had raised a large field army of Greek mercenaries and overrun Babylonia and Media.7 In the spring of 129 BC, Phraates ambushed Antiochus and his royal bodyguard outside of Ecbatana (today Hamadan). Antiochus committed suicide; his Greek mercenaries offered their services to Phraates. Phraates succeeded beyond all expectation. By his unexpected victory, Phraates not only ended future Seleucid threats, but he also confirmed Parthian rule over Iran and Mesopotamia. The Upper Euphrates henceforth marked the western boundary of the Parthian Empire. Meanwhile, the ever-colorful Demetrius returned to his capital and plunged what was left of the Seleucid Empire into civil war.8 As for the jilted Rhodogune, she lived on in legend as a valiant warrior princess neglected by her cad of a husband. She captured the imagination of French dramatists and painters in the seventeenth century. She is depicted on the canvas in the company of Cleopatra, both of whom shared the fate of marrying foreign husbands too ambitious for their abilities.9 Pierre Corneille, a master of turning Classical legend into French drama, composed the tragicomedy Rodogune to the delight of the court of Louis XIV.10 Unfortunately for Phraates, he did not long enjoy his victory. He fell fighting new invaders from the east, the Iranian Sacae, driven from their Sogdian homeland by the Tocharian-speaking Yuezhi. Antiochus’s Greek mercenaries betrayed their new paymaster at the critical moment in the battle, and defected to the Sacae.11 Fortunately for Phraates’s successors, the Sacae turned southeast into the Helmand valley, and then crossed into India.

Mithridates II (124–87 BC), a cousin of Phraates II, transformed the Parthian kingdom into an empire. He adapted Seleucid and Achaemenid bureaucratic practices to tax a far greater state than any of his predecessors had ruled. The wealth of his empire lay in the cities of the Fertile Crescent stretching from the Red Sea to the Eastern Mediterranean, the cradle of Eurasian urban civilization.12 Great Greek and Aramaic merchant families at Babylon controlled the banking and commerce of the Near East. Babylonia was the most densely populated region of the Near East outside of Egypt. The land was crisscrossed by an irrigation system that each year yielded windfall harvests of cereals, fruits, and vegetables.13 Mithridates also controlled the central section of the Silk Road, and so he taxed caravans traveling between Palmyra and Maracanda (Samarkand) as they passed through his realm.14 The route was both well-known and without an alternative. The Greek geographer Isidore of Charax a generation later described meticulously the distances between stations, water sources, and markets along the route.15 Mithridates thus forged a bureaucratic empire that provided the revenues to hire horse archers from among nomadic allies on the central Eurasian steppes, and to reward a landed Parthian warrior caste that furnished heavy cavalry (cataphracti) under the terms of feudal arrangements.

Foremost, Mithridates, as a nomadic conqueror, needed legitimacy for his pretenses to being the newest King of Kings in the Near East. To this end, he took two measures, namely creating an ideology to exalt his kingship, and building a new capital to serve as the theater for the ceremonies of this ideology. Parthian silver coins, drachmae, provide our best guide as to how Mithridates shifted his stance from a nomadic warrior king to the Great King. On their silver coins, drachmae, Arsaces, eponymous founder of the dynasty, and his immediate successors are depicted as clean-shaven princes of the steppes clad in the bashlyk, a soft felt cap with flaps designed to protect the head from the extremes of temperature on the Eurasian steppes.16 Mithridates presented a new portrait; he sports a long, neatly groomed beard, the mark of virility since the first conqueror Sargon of Akkad. Mithridates, on his earliest coins, wears the pearl diadem popularized by Alexander the Great and adopted by Hellenistic monarchs.17 Then, on later coins, he exchanges the diadem for a tall, bejeweled tiara of the Great King of Persia. He is shown as clothed in silk ceremonial robes sewed with pearls and jewels.18 On the reverse of his coins, Mithridates retains the conventional figure of his ancestor Arsaces, clad as a steppe warrior with bow and arrow, but henceforth, Arasces is enthroned in the fashion of a Near Eastern monarch rather than seated on the omphalos.19 The Arsacid kings had adapted this reverse type from the Seleucid kings, devotees of Apollo, who had depicted on their coins the god as an archer seated on the omphalos, the stone at Delphi, representing the navel of the world. Engravers, trained in the Greek artistic tradition, cleverly refashioned a divine scene into a royal one. In keeping with their conceit as philhellenes, Parthian kings used Greek for their coin inscription. With Mithridates II, the coins proclaim each Arsacid ruler King of Kings.

A weathered rock relief, perhaps commissioned by Mithridates’s son, survives at Behistun, which is on the western edge of the Iranian plateau, east of the Zagros Mountains, near the modern Iranian city of Kermanshah.20 The limestone cliffs overlook the royal road from Ecbatana to Babylon so that any visitor could not fail to see the monumental reliefs carved on the cliffs. On his relief, Mithridates is attired in his new regalia, and accompanied with four loyal governors; the Greek inscription is mostly lost. The relief is but a modest version of the nearby awesome, trilingual inscription of Darius I, who in his relief receives twelve subservient rebel monarchs and lists his deeds. Even so, the casual visitor was expected to associate the two monarchs as the righteous King of Kings.

Like any ruler of nomadic origin, Mithridates appreciated the silk and exotic gifts that enhanced his prestige in the eyes of his subjects, and provided rewards to loyal Parthian nobles and vassal princes. At some date soon after 115 BC, the Chinese historian Ban Gu reports that a Parthian king, undoubtedly Mithridates, welcomed envoys of the emperor Wudi with an escort of twenty thousand horsemen, and then feted the envoys at his capital.21 In return for the costly silks of China, Mithridates sent the envoys home loaded with gifts, including ostrich eggs, and accompanied by magicians, most likely Zoroastrian priests. Arsacid kings prized Chinese silk, rubies and emeralds of southern India, and pearls harvested from the Red Sea. All were necessary for the ceremonial costumes and display projecting the power of the Parthian monarch at his new capital, Ctesiphon. For Mithridates, just like Kublai Khan twelve centuries later, required a great city to awe his new subjects. Hence, Parthian Ctesiphon and Mongol Shangdu, better known as Coleridge’s Xanadu, served the same purpose.

Mithridates chose to build his new capital at Ctesiphon, today twenty miles southeast of Baghdad. The city occupied an island and its opposite east bank in a sharp bend of the Tigris River, and it was directly across from the Greek city Seleucia ad Tigrim.22 Mithridates likely never considered alternatives that were ruled by vassal princes: Persepolis, the Achaemenid ritual capital; Susa, the Persian administrative capital; or Charax, the leading port on the Persian Gulf. The Arsacid kings held their winter court at the palace in Ctesiphon, where they received foreign delegations. Successive Parthian kings and Persian shahs expanded and beautified the city, building additional palaces, a vast park housing caged lions and elephants, and a wide processional avenue that ended at a grandiose audience hall.23 By the mid-fourth century AD, the city, its suburbs, and Seleucia had merged into a sprawling metropolitan center twice the area of imperial Rome. The markets of the Greek city Seleucia supplied the daily needs of the residents of the Twin Cities that might have peaked at over one million. The cosmopolitan city thrived and was graced with royal architecture that fused Hellenic and Near Eastern traditions. Merchants and craftsmen from across Eurasia flocked to the city. Scholars, religious thinkers, and philosophers found an exciting intellectual life in a city that was home to Zoroastrians, Christians, Jews, Manichees, Buddhists, and worshippers of the ancestral gods of many peoples.

Unfortunately, nothing of the Parthian city survives aboveground because the Sassanid shahs remodeled and built over the Parthian city between the third and seventh centuries AD. Yet the ruins of the Sassanid audience hall, dubbed in Arabic Tāq Kasrā, and later Persian Medieval accounts give us a glimpse of how envoys must have been awed as they made their way to the throne room of a Parthian king.24 In the sixth century, envoys would have traveled down wide colonnaded boulevards, passing vast parks stocked with wild animals. Guards in ceremonial silver-or gold-plated armor lined the final approaches to the audience hall. Once inside, the envoys saw a vast rectangular hall supported by monumental baroque colonnades. The notables of court stood in ranks, arranged by their social rank and identified by their distinct robes and headdress. At the far end, under a great vaulted ceiling reaching 110 feet (30 meters), stood the shah’s golden throne on a raised platform. At a lower level, to the right, behind, and to the left of the shah’s throne, were lesser, empty ones representing the emperors of China, the Roman emperor, and the Hephthalites (the successors to the Kushans). Sassanid shahs were masters of diplomatic ceremony so that they undoubtedly articulated and innovated on earlier Parthian royal rituals. They upheld an ideology based on their Persian heritage and the Zoroastrian faith, whereas Parthian kings tolerated all faiths and styled themselves as patrons of Greek culture and cities. Even though only brief descriptions of the Parthian palace have survived, Mithridates and his heirs employed comparable rituals to promote their ideology as heirs of both the Persian Great King and Alexander the Great. Even more significant, Mithridates made Ctesiphon the imperial center of the Near East for the next seven centuries. Yet in constructing Ctesiphon, Mithridates unwittingly made his empire vulnerable to attack. At the end of his reign, Mithridates failed to perceive the danger posed by the Roman Republic. In 92 BC, his envoys abased themselves in supplication before L. Cornelius Sulla, the Roman governor of Cilicia (today southeastern Turkey). The proud Sulla, seated atop his tribunal, bestowed as a favor to Mithridates the friendship of the Senate and Roman people. Mithridates was outraged and ordered the envoys severely punished. The incident was the opening of a strategic clash between Parthia and Rome.

The later Parthian kings found their empire flanked by two dangerous rivals: Kushans to the east, and the Roman Republic to the west. Rome proved the deadlier foe. Parthian cavalry twice thwarted Roman invasions. At Carrhae, Parthian cavalry annihilated Crassus’s legions; in 36 BC, they repelled an invasion by Mark Antony.25 Once Augustus founded the Roman Empire, the balance of power shifted decisively in Rome’s favor. Augustus transformed the legions of the Republic into a professional imperial army unequaled on the battlefield and possessing superb engineering and logistics. Augustus also hit upon a winning diplomacy against the Arsacid king and thereby at minimal cost secured his eastern frontier on the Upper Euphrates River. Augustus avenged the defeat of Crassus, at least to the satisfaction of his poets, and restored Roman honor thirty-three years later, in 20 BC. He threatened the then reigning Parthian king, Phraates IV, with an invasion if Phraates refused to return the legionary standards and prisoners of Crassus’s army.26 The imperial army would have easily marched down the Euphrates and sacked the Twin Cities of Ctesiphon and Seleucia ad Tigrim. Phraates folded. He could not possibly resist the imperial army under M. Vipsanius Agrippa, Rome’s most talented commander and the emperor’s devoted comrade in arms. Furthermore, over the past thirty years, the Romans had mastered the art of fighting against Parthian horse archers.27 The aged survivors of Crassus’s army returned home from a dreary exile on the edge of the Karakum Desert, where they had been posted to mount guard against nomadic tribesmen. The legionary eagles were eventually housed in a massive Temple of Mars Ultor (the Avenger) in the new forum of Augustus. Poets, historians, and artists went to great lengths to hail a diplomatic settlement as a victory. Augustus knew better.28 He had exploited Phraates’s difficulties with rivals to his throne to extort a symbolic concession. In return, Augustus sent a delegation of senators who hailed Phraates as a friend of the Roman people. They also conveyed many exotic gifts, foremost a renowned courtesan (hetaira), Musa Urania. The heavenly Musa (as Augustus had anticipated) so dazzled Phraates with her charms and wit that the smitten king made her his principal wife and consort.29 She soon bore Phraates a son. The king recognized his son, Phraates V, as his heir in preference to his other sons who had been handed over as hostages to Augustus. Musa intrigued incessantly. In 2 BC, she had her husband poisoned and assumed the regency for her adolescent son.30 She wielded extraordinary power, for she is the only Parthian queen whose portrait appears on coins. The Chinese historian Fan Ye in the Hou Hanshu reports this as a curious fact based on travelers’ reports.31 Mother and son botched a war in Armenia and were overthrown by the nobility, who then warred among themselves over the succession for the next thirty years.32

The emperor Augustus had discovered the Parthians’ strategic weaknesses, which he could exploit to Rome’s advantage. No Arsacid king could afford to risk his capital or Babylonia. Although the Parthians ruled a Near Eastern Empire, they remained children of the Eurasian steppes, and so prone to war over the choice of kings based on the principles of lateral succession. A Roman imperial army threatening to invade Babylonia and to incite civil war among family rivals could quickly compel any Arsacid king to negotiate. But the principles of lateral succession complicated the family politics of the Arsacid house. Each Arsacid king had to provide lesser realms for his brothers, nephews, or cousins. Armenia, vital to the defense of the Roman East, became the cockpit of wars because Arsacid kings sought to place their younger kinsmen on the Armenian throne.33 Rome insisted that any king of Armenia owed his crown to the Roman people ever since the imperator Pompey the Great had restored King Tigranes the Great to his throne in 66 BC.34 The proud Armenian nobles—nakharars, to use their Medieval name—shared with their Parthian counterparts the same martial ethos, passion for hunting, and keen sense of personal honor.35 Most of them preferred an Arsacid prince as their king over any candidate dispatched from Rome, who aped the arrogant manners and dress of a Roman senator. Inevitably, Rome and Parthia clashed in seven major wars. Each time, the imperial legions eventually triumphed over the Parthian cavalry, and three times Roman legions sacked the Parthian capital of Ctesiphon.

Throughout this strategic rivalry, neither the Roman emperor (with the exception of Trajan) nor Parthian king aimed to destroy the other’s empire, but rather they contested control over the strategic routes across Armenia and the grasslands of northern Mesopotamia between the Upper Euphrates and Tigris Rivers, known today by its Arabic name, al-Jazirah.36 From Rome’s perspective, the cities and irrigated fields of Mesopotamia could support Roman provincial administrations and legions. The high plateau of Armenia was best left to a vassal king, but any king acceptable to Rome was unpopular with his nobility. For the Arsacid king, his strategic task was far easier. In Mesopotamia, the Parthian king easily won over Aramaic-speaking princes of the cities, who doubled as tribal rulers of the surrounding Bedouin tribes.

For two generations, no Arsacid king dared to challenge the settlement of Augustus. In 53, a charismatic king Vologases I ended a generation of civil war, and placed his younger brother Tiridates on the throne of Armenia. In the autumn of 54, the new emperor at Rome, Nero, sent as commander of an expeditionary force Gnaeus Domitius Corbulo with instructions to oust Tiridates from Armenia.37 Corbulo, hailed the finest of imperial commanders by the senatorial historian Tacitus, brilliantly accomplished his mission, and so earned the jealousy of Nero.38 This War of the Armenian Succession (54–66) ended in a sensible settlement whereby Tiridates ruled in Armenia, but received his crown from Rome.39 Nero hosted Tiridates at a spectacular celebration that magnified the power of Rome. During the festivities, Tiridates quipped that never was so malevolent a monarch, Nero, served by so noble a general, Corbulo.40 Tiridates returned to rule Armenia as a dutiful Roman client, whereas Corbulo was later forced to commit suicide on orders of Nero or face trumped-up charges of treason.

Both Nero and Vologases had avoided direct conflict, but the later Flavian emperors took measures to ensure Roman supremacy in any future war with Parthia. Rome henceforth stationed legions on the Upper Euphrates, and built across Asia Minor depots, bridges, and highways.41 In 113 AD, another Armenian crisis erupted when the Parthian king Osroes I crowned his nephew king of Armenia in violation of the settlement of 66. Osroes calculated that his opportunistic action might result at most in another proxy war in Armenia.42 Instead, in the next year, the emperor Trajan, the greatest of all warrior emperors, took the field at the head of an expeditionary army of over one hundred thousand. Osroes was stunned by the speed and scale of Trajan’s invasion. In the next two years, Roman legions overran Armenia and Mesopotamia. In 116, Trajan deployed the logistics and strategy perfected in the Dacian Wars. Two Roman columns, marching down the Tigris and Euphrates, converged to storm and sack first Seleucia ad Tigrim, and then Ctesiphon.43 Osroes fled east over the Zagros Mountains. Trajan reached the shores of the Persian Gulf, where he navigated the waters and contemplated repeating Alexander’s march to India. But the emperor, age sixty-two, was weary from a life of tough campaigning. He received alarming news when he put ashore.44 The Parthian client prince of Adiabene in northern Mesopotamia had rebelled. More bad news soon followed.45 The Jews of Cyprus, Egypt, and Cyrenaica revolted under an obscure figure, Loukas, who claimed to be the Messiah of the House of David.46 Trajan returned north to deal with these threats, but he died suddenly at the sleepy town of Selinus on the southeastern shore of Asia Minor on August 19, 117. His cousin and heir Hadrian, to his credit, judged his abilities correctly. He could not manage major rebellions and a war of conquest at the same time. He withdrew Roman forces to the west of the Euphrates, and concentrated the legions against the rebels. Armenia was returned to a client king.47 King Osroes, amazed by his good fortune, rallied the Parthians, expelled the pro-Roman Parthian king in Ctesiphon, and recaptured Babylonia and Mesopotamia.48 From the start, Trajan pursued a strategy of overthrow, aiming to annex as provinces Armenia and Mesopotamia and to impose a compliant king on the Parthian throne ruling over Babylonia and Iran. It is doubtful that the Arsacid monarchy could have survived as a great power had Trajan lived to consolidate his victory.

In withdrawing from Trajan’s conquests, Hadrian has been praised by modern scholars for his prudence in recognizing that the empire was overextended.49 Yet he acted more out of expediency than strategic design. At the time, the move was extremely unpopular and precipitated a plot by four of Trajan’s senior generals. Subsequent events would prove that Trajan was correct, and Hadrian was wrong, on the imperial boundary in the Near East. Roman security in the East required control of the highways across Mesopotamia between the upper Euphrates and the Tigris. This meant future wars with the Arsacid kings were inevitable.

In 161, another able Parthian king, Vologases IV, challenged Rome’s right to appoint the king of Armenia, when he received news of the accession of two untested emperors, Marcus Aurelius and Lucius Verus. The war initially went in favor of Vologases, whose horse archers destroyed a Roman legion, and expelled from Armenia the king C. Julius Sohaemus, a polished Roman senator widely unpopular among his subjects.50 Two years later, veteran Roman commanders coordinated offensives in Armenia and Mesopotamia that reversed the situation. Lucius Verus, the indolent adoptive brother and son-in-law of Marcus Aurelius, was dispatched from Rome to oversee these operations. Lucius Verus, however, never made it to the field, but rather lingered in Antioch, capital of Roman Syria and third largest city of the empire. Lucius Verus preferred the pleasures of the city and the charms of his mistress, the courtesan Panthea, to the neglect of his wife, his co-emperor’s daughter. The most talented among the commanders, C. Avidius Cassius, repeated Trajan’s march into Babylonia and sacked Seleucia and Ctesiphon.51 His victorious soldiers returned to Rome infected with a plague which has sometimes been classified as the first pandemic, which came out of China and swept Eurasia.52 Avidius Cassius gained top honors for winning this war, but he later erred in staging a revolt against Marcus Aurelius, and was forced to commit suicide.53 In 169, Lucius Verus, to the relief of Marcus Aurelius, died from the plague.

For Vologases, this war was almost as disastrous as the one against Trajan. Rome annexed the region immediately east of the Euphrates, Osrhoene, and so controlled the strategic crossings across the Euphrates. The kings of Osrhoene and Armenia were permitted to keep their thrones as friends of Rome.54 Less than a generation later, the emperor Septimius Severus, in two successive Parthian Wars waged between a major Roman civil war, extended the Roman province of Mesopotamia to the Upper Tigris River, stationed two legions in the province, founded Roman colonies, and built highways. In the second war, Septimius Severus invaded Babylonia, and sacked Ctesiphon for a third time in January 198.55 Henceforth, the Arsacid king faced the strategic nightmare that, in any future clash with Rome, the legions could easily invade from bases in northern Mesopotamia and sack the Twin Cities, the financial hub of the Parthian Empire.

For two generations, Rome and the Parthians had clashed over the mastery of the Near East, and in 200, Rome had emerged as the victor. During this period, the Arsacid king was hard-pressed to meet the threat from Rome as well as another one from the Kushan emperor to the east. Wars over the succession prevented kings Osroes and Vologases V from countering Trajan or Septimius Severus. In 214, the emperor Caracalla, son of Septimius Severus, marched east in yet another Roman invasion during a civil war between Arsacid brothers.56 This time, the emperor acted out of impulse rather than strategic reasons. Caracalla, savage in nature and prone to fits of rage, longed to emulate Alexander the Great by conquering the Parthian Empire. He even proposed to marry the daughter of Vologases VI, one of the Parthian contenders. For, after all, Alexander had married Persian princesses. Caracalla and his court took over two years to reach the front, because they were too busy playing tourists among the celebrated Greek sanctuaries and cities. In 216, Caracalla waged a limited offensive across the Tigris, and withdrew to winter at Carrhae. On April 8, 217, the emperor was ignominiously murdered while relieving himself in the bushes near Carrhae on orders of his Praetorian prefect Macrinus.57 Macrinus was declared the new emperor, and concluded with Artabanus V, the victor of the civil war, a peace confirming the status quo ante bellum.

Even though the assassination of Caracalla cut short the Roman invasion, the mere threat of a fourth sack of Ctesiphon fatally compromised Artabanus V. Ardashir, the Sassanid king of Persis, was emboldened to rebel against his Parthian overlord.58 In 224, Ardashir defeated and slew Artabanus V. Three years later, he entered Ctesiphon, where he was crowned in the Parthian palace as King of Kings of a new Persian or Sassanid Empire. The Sassanid shahs, under the banner of a militant Zoroastrian, proved far more deadly rivals of Rome, for they aimed to restore the empire of the Achaemenid kings of Persia. For the next four centuries, Imperial Rome and Sassanid Persia fought themselves to mutual exhaustion in their struggle for the mastery of the Middle East.

It is often pointed out that Rome ironically undermined a Parthian rival to the benefit of a far deadlier foe, the Sassanid Persians. Hence, in the nationalist hagiography of Iran today, the Parthians are dismissed as interlopers who were neither victorious nor pious Zoroastrians. Yet, in contesting Roman advances into the Middle East, the Parthians defined the eastern limits of Roman imperial power. They thus proved worthy imperial rivals to Rome. Even more significantly, the Parthians defined, for the first time, the geopolitics of the Middle East that have dictated the course of strategic rivalries in this region down to the present day. The Arsacid king drew on the resources of Iran and the Central Eurasian steppes to oppose a far stronger power, Rome. Rome, however, was a Western power based in the Mediterranean world, and she could not impose her hegemony over the entire Middle East in the face of an effective Iranian power, the Parthians. Any power with its base outside the Middle East faces the same challenge. Each succeeding Western power has to come to terms with the regime in Iran, which sees its legacy as including the historic lands of Iraq, Afghanistan, and Transoxiana. In the sixteenth and seventeenth centuries, the Safavid shahs of Iran similarly checked the Middle Eastern ambitions of the Ottoman sultans of Constantinople, whose empire was based in the Balkans and Anatolia. Since the nineteenth century, first the British and then the Americans have had to reckon with Iran in any strategic policy. And so the Parthians, the offspring of Eurasian steppe nomads, have left their imprint on the world politics of today.