A new attempt to place a son on the throne in Armenia angered Rome, which, with the aid of the nobility, sent for Tiridates III, a pretender the barons had crowned at Ctesiphon. Artabanus was forced to take refuge with the Dahae, who helped him win back his throne. In 37 a meeting with a representative of Rome on a bridge in the middle of the Euphrates allowed an agreement to be reached that maintained the status quo in Armenia and recognized Parthian sovereignty with the river as the frontier. Artabanus, a strong personality, did not seek to impose his kingdom as a world power, but he did not hesitate to make plans to regain the western provinces, the former Achaemenian possessions. Dissolution of the Parthian state
The period from 51 to 122 is one in which the Parthian state slowly dissolved and decomposed into several small countries, and various parties lay claim to the throne—an inevitable result of the weakness of the central power. In the 1st century ad the Parthian empire, according to the Roman historian Pliny, was composed of 18 kingdoms, 11 in the north and seven in the south, some governed by Arsacid princes and others by local dynasties. In 58 Hyrcania became independent. In the realm of external affairs, an effort was made to maintain good relations with Rome, especially because of the new kingdom of the Kushān, which was causing concern on the eastern frontiers. It might be for this reason that in 87 Parthia sent an embassy to neighbouring China to the east of the Kushān. Internally, the ethnic upsurge became more accentuated.
After the short reign of Vonones II (51), the throne passed to Vologeses I (reigned 51–80), an ardent anti-Roman. One of his brothers, Vonones, was made king of Media. Vologeses I wanted his second brother, Tiridates, to be king of Armenia—putting him in position to break with Rome, which opposed him militarily. Upon orders from Nero, the Roman general Corbulo secured Armenia, but his operations were broken off by the exchange of ambassadors. An agreement was finally reached: in 66 Tiridates left for Rome with his whole family, surrounded by a retinue of princes and 3,000 Parthian nobles. He received from Nero the crown of Armenia. Parthian control and the end of hostilities were announced by closing the doors to the Temple of Janus.
Nationalist sentiment—which had been expressed under Artabanus III in a genealogical table invented to prove the Achaemenian descent of the Arsacid house—also manifested itself under Vologeses I: the Avesta, the holy book of the Iranians, was compiled, and coins were issued on which, for the first time, Pahlavi (Middle Persian) characters were added to the Greek legend.
In 78 Pacorus II came to the throne, to be supplanted in 79 by the ephemeral Artabanus IV (80/81), who was then replaced permanently by Pacorus II. During his reign the country showed signs of a profound decomposition. The barons refused to obey the crown. In the provinces the army and the finances were in the hands of the nobility. Aristocrats occupied the highest positions, which became hereditary. Plots with Rome were hatched, and the nobility felt itself the equal of the dynasty, ready to revolt in defense of their privileges. Externally, the dynasty was unable to count on Rome, which constantly plotted in support of new pretenders. In 109/110 Pacorus II was eclipsed by Osroes, his brother or brother-in-law, but he maintained limited power until his death in 115/116.
In 114 the emperor Trajan invaded Armenia. In vain did the king put his crown at Trajan’s feet—he was defeated by the Roman soldiery. With Armenia occupied, the emperor descended with his army into Mesopotamia. All of Babylonia was taken, and Ctesiphon, the capital, fell into the hands of the Romans, who carried off a daughter of Osroes and the golden throne of the Parthian kings. Victorious, Trajan went as far east as the Persian Gulf. Iranian reaction was not long in coming. Faced with the gravity of the Roman offensive, all the princes of the royal house, formerly divided by internal strife, united against the invader. At Ctesiphon Trajan crowned a new vassal king, but revolt was in the wind, and attempts to disunite the Parthian chiefs failed. The Romans suffered losses, and, after a reverse on the walls of Hatra, Trajan abandoned the campaign and died on his way home. Trajan’s successor, Hadrian (reigned 117–138), abandoned all pretensions to Armenia, Mesopotamia, and Assyria.
Hadrian’s desire for peace seems to have been sincere. He sent back Osroes’ daughter, promised to return the golden throne, and did not try to profit from the long power struggle between Osroes and Vologeses III (or II). He even invited Osroes to come to Rome. Peace with Rome
Thus ensued four decades of peace with Rome. The status quo it maintained with its western neighbour seems even to have been a necessity for Parthia, the expansion of the Kushān kingdom on the eastern frontiers having reached the peak of its power under King Kaniṣka (Kanishka). Accurate information about the relations between the Kushān and the Parthians is not available, but this long peace sought with Rome suggests that certain precautions were necessary for the kingdom of Iran. The end of the Parthian empire (162–226)
The 40 years’ peace was succeeded by almost uninterrupted hostilities with Rome, with varied success; Parthia was more vulnerable because of the exposed position of its capital.
The reigns of Vologeses III (or II; c. 105/106–147?) and especially Vologeses IV (or III; 148–192), the latter not having to dispute the throne with a pretender, could by their lengths be a sign that the country might have experienced a certain stability. But underneath the apparent calm the intrigues continued, with Rome receiving embassies from the Hyrcanians, the Bactrians, and doubtless from the Kushān.
A new clash with Rome came in 161, this time on the initiative of Vologeses IV (or III), who considered himself strong enough to attack. He occupied Armenia, crossed the Euphrates, and invaded Syria, which for two centuries had not seen Parthian cavalry. And, although the country had been Roman since the time of Pompey, the Syrian population, which included Jews driven from Palestine by the Romans, received the Parthians as liberators. The situation became so serious that Lucius Verus, co-emperor with Marcus Aurelius, was dispatched to the east with strong reinforcements taken from the fronts on the Danube and the Rhine. The Romans retook Armenia (163) and succeeded in a campaign similar to Trajan’s: Dura-Europus was taken and remained Roman until its destruction by the Sāsānids; Seleucia on the Tigris, despite the welcome it reserved for the Romans, was sacked; and in 164 or 165 for the second time Ctesiphon fell into the hands of Romans, who razed the royal palace.
Once more success was not continuous. The Roman army had come from Armenia and crossed through Azerbaijan, where it was exposed to plague. Contaminated, the Roman army was sorely tried by disease and obliged to retreat, but not definitively. Lucius Verus, repeating his campaigns in Armenia and northern Mesopotamia, inflicted heavy losses on the Parthians.
The tensions between the two states did not diminish when Vologeses V (or IV; reigned 191–208/209) supported a pretender (Pescennius Niger) against Septimius Severus. The latter became emperor in 193 and began operations that permitted him to occupy first northern and then southern Mesopotamia and, for the third time in a century, Ctesiphon. The Parthians in their retreat adopted a scorched-earth policy. As under Trajan, the starving Roman army went back up the Tigris, failed in its attempt to take Hatra, and left the country.
Vologeses VI (or V), son of the previous king, succeeded him (reigned 209–c. 222), but his throne was contested—and the empire divided (see below)—from 213 on by another prince, Artabanus V (c. 213–224), who was able to maintain his claim with the support of the kingdom of Media (see table for chronology). A new Roman invasion of Mesopotamia took place under Caracalla, the casus belli being the refusal of Artabanus V to give Caracalla his daughter in marriage. The young emperor dreamed of rebuilding Alexander’s empire but succeeded only in pillaging Media and destroying the hypogea of the Arsacid kings at Arbela. The Parthian reply was harsh. Artabanus avenged himself by invading the Roman provinces and destroying several cities. Rome sued for peace. Artabanus’s conditions were too hard and were refused. Hostilities were taken up again and once more turned in favour of the Parthians, who were so successful that the emperor Macrinus paid a large sum to make peace.