Parthian control in Mesopotamia was weak, and dynastic squabbles made it even weaker, so there were various provincial kingdoms which flourished in the 1st century. Among these was Adiabene, which had its capital at Erbil. Adiabene has received special historical attention because of the unique conversion of its leadership to Judaism.
Helen was married to her brother, the Adiabene king Monobazus I. The traveling Jewish merchant Hananiah (Greek Ananias) got access to certain women at the court and taught them to worship in the Jewish manner. Subsequently, he converted Helene and the king as well. Her son Izates, the heir-apparent, was living in Charax Spasinu on the Persian Gulf for safety from the jealousy of his half-brothers. He was likewise converted by another merchant.
Not only did the royal family convert, but they were generous patrons of projects in Jerusalem and improvements at the Temple. When the First Jewish Revolt erupted in Jerusalem, the Adiabenes were at the forefront of the fighting. Unfortunately, their history fades into obscurity after the First Jewish Revolt -- when the light of Josephus and the Talmud turn from them -- and after the Romans sacked Erbil in 116 CE, it is likely the dynasty ended. After that, Adiabene existed only in name as a province.
Our knowledge of the Adiabene kingdom mostly comes from Josephus and the Talmud.
The conversion can be framed politically. Although legends exist of the family's religious fervor, their Judaism also was very politicized. The Adiabene leadership became pioneers in not only supporting the Jews in Jerusalem but also helping lead their revolt against the Romans. The political narrative can be understood internationally, in the rivalry between East and West that was then being played by the Romans and Parthians; nationally, in the opportunity for Adiabene to build alliances with other Jewish city-states in the Parthian empire; and locally, in the already substantial Jewish population in Adiabene when the rulers converted.
Internationally, this can be understood via the dichotomy between West and East, within which Adiabene was sandwiched by Rome and Parthia. There was no indication of animosity between Jews and Persians, nor of particular closeness. Sometimes local Jewish rulers would agitate against Parthia for autonomy, or otherwise prove themselves to be bad vassals. However, this was the case for almost any city-state. Persians had historically tolerated Jewish religion, allowing its practice and the return of Jews to Canaan if they so pleased (having been exiled by Babylonians). But this tolerance was not philosemitism: it was a principle extended to all the empire's myriad religions. The only shift -- and one in Adiabene's favor when it converted to Judaism -- was that at the time of the conversion, the Jews in Canaan were bristling against Roman rule and their revolt against Rome was on the horizon. Thus, for the Persians the Jews were the enemy of the enemy.
Conversion to Judaism allowed Adiabene to build strong ties with other Jewish city-states at a time when the future was uncertain. Dynastic struggle had weakened Parthia and its central government was failing outside the Persian heartland. There were still obedient satrapies (provinces) adhered to the central government, but there were also provincial Jewish and Greek kingdoms in Babylonia who varied as vassals or rebels, as well as an Armenian kingdom to the north. Adiabene was a kingdom, but as a loyal vassal it did not challenge Parthian hegemony.
In Babylonia, large numbers of Jews were settled. At Nehardea, there had been a local Jewish kingdom (from 20 to 35 CE) ruled by the brothers Anileus and Asineus, which Parthian king Artabanus III had negotiated with and recognized. Near Seleucia-on-the-Tigris, the Jews there had established a pseudo city-state. In nearby Armenia, there had been Jewish dynasts who held brief power, claiming descent from Herod the Great. Chalcis, Cappadocia, Iturea, Abilene, and of course Canaan had all had Jewish dynasties. In fact, the Armenian king Tigran deported Jews from the Adiabene region to Armenia to help develop the economy there.
Parthia's hegemony was fluctuating. Adiabene was faced with two choices: pursue strength and power to secure its survival in a post-Parthian landscape; or remain close to Parthia and position itself as a steadfast ally. On the one hand, alliances with other local dynasties would be essential -- especially being the leader of such alliances. However, if Parthia reasserted its hegemony it would surely squash politically threatening leaderships. Adiabene navigated this political tightrope. It formed alliances and consolidated its diplomatic power. However, by forming specifically Jewish alliances with the Jewry of Canaan and Babylonia, Adiabene was also strengthening Parthia'a western frontier against antisemitic Rome. Put simply, a Jewish Adiabene was growing strong enough to hold and wield authority post-Parthia, but was also giving Parthia a protective Jewish frontier.
Monobazus I must have seen the Jewish rebellion in Jerusalem as a promising enterprise. It was by no means impossible that the Canaanite Jews would flex their military might and regain independence from Rome. If the revolt were to succeed, then Adiabene could perhaps secure the throne of an independent Canaan through its active war support, earlier philanthropy to Jerusalem and its people, royal status, and support mustered from the Persians. Also, Adiabene's location would serve it well as a royal capital, as the gateway from the Mediterranean to Armenia and Persia.
Within Adiabene, the conversion to Judaism did have negative political consequences among the nobility. Josephus attests that the royal family feared the nobility's disapproval of their conversion and circumcision. Some of the nobility even went to support Izates' enemies. However, as a whole Adiabene itself already had many Jews.
Of note, Adiabene was not the only time that merchants had effected the conversion of a monarchy to Judaism, as it happened in Edessa in the next century. Also, Monobazus would not be alone in changing religion for political gain. The Arsacid rulers blatantly did so when they abruptly converted from Hellenistic practices to Zoroastrianism in a bid for Persian support.
Adiab - Jerusalem relations
After converting to Judaism, Adiabene aggressively supported the Jewish cause in Canaan and the royal family maintained close ties with Jerusalem. They made great efforts to impress Canaanite Jews with their loyalty, benevolence, and generosity. They donated lavishly to the Temple, and to the people in times of famine. They especially impressed the Pharisaic party with their loyalty to its interpretation.
The Jewish War in Palestine erupted. Parthia herself did not intervene nor did Babylonian Jews volunteer support. On the other hand, the Adiabene royalty was well-represented in the opening campaign and remained loyal to the zealot cause until the end. Adiabene encouraged the revolution of 66, and led the opening action against Cestius, which precipitated the complete broke between Rome and Judea.
Surely Parthian king Ctesiphon did not mind having a sort of proxy in its fight against Rome. However, Parthia did not get involved in the Jewish revolt in Canaan. This is likely because there was a fragile peace to maintain with Rome. Just a few years earlier, a treaty had been signed between Rome and Parthia after warring in Armenia. Supporting the Jews would endanger this peace and catalyze renewed war with Rome along their contact borders. Parthian king Ctesiphon could not expect Parthia's treaty with the Romans to stand if he supported the revolutionaries. However, on the other hand they did not object to Adiabene action. It was expedient to let the Adiabense do what the Parthian government could not. They must have known the threat Roman success could pose to the persian heartland.
Adiabene history is largely a mystery, but eventual excavations at its capital Erbil might unearth more.
reigned ? - 20s CE
Izates I was king of Adiabene around 15 CE, but otherwise nothing is known of his life besides he was the father of Helena and Monobazus I.
c 30 CE
reigned 20s - 31 CE
Monobazus was king in the 20s and 30s. He was married to his sister Helena, and together they had at least two sons: Izates II (the heir-apparent) and Monobazus II.
lived ? - 50s CE
She may have been the intermediate ruler at times, such as when her husband died or son died.
lived c 1 - c 55 CE
After his conversion, Izates succeeded to the throne. Nisibis. He reigned for 24 years, usually pinned from 31 CE - 55. He became involved in turbulent Parthian succession politics. In 36 CE, the Parthian king Artabanus III was deposed by the nobility. Izates supported him, and when he returned to power in 36 CE he rewarded Izates by ceding Nisibis and surrounding territories to him (which had been held for a time by Armenia).
During the next few years' complicated dynastic struggles through the accession of Vologases I in 51 CE, Adiabene was repeatedly threatened by invasion by one or another contender, without significant result. Roman king Corbulo's invasion in 57-58 CE resulted in his capture of Armenia by 60, and the Roman appointee Tigranes V ravaged Adiabene. Vologases hastened to Adiabene to support the threatened satrap. After indecisive fighting, Corbel accepted a peace agreement with the Parthians and their Adiabenian allies at Rhandeia in 63 CE.
Adiabene was taken from Parthian suzerainty by Tigran, but Phrases regained it in 64 BC.
38 CE • Deposition of Artabanus, struggle of Gotarzes and Vardanes.
43 CE • Taking of Seleucid.
44 CE • War of Vardanes against Izates.
45 CE • War of Gotarzes and Vardanes.
46 CE • Vardanes murdered, war ends with Gotarzes as unopposed ruler.
47 CE • Mithridates versus Gotarzes.
48 CE • Izates goes over to Gotarzes against Mithridates.
49/50 CE • Gotarzes dies, Vonones ascends the throne.
50/51 CE • Vologases succeeds Vonones.
56/57 CE • Outbreak of war between Vologases and Izates. Hyrcanians invade, and Vologases abandoned the project.
reigned c 55 - ?
He ascended the throne after his brother Izates II died. It is known he remained king through the First Jewish Revolt.
There was already a civilian Jewish population when the royal family converted. Neusner (1964) argues that Nisibis was a Jewish community as large and significant as in Babylon to the south, on the basis of records suggesting it made Temple contributions, making it the only other Jewish center along the Euphrates besides Nehardea in Babylonia to do so.
Nisibis contained a Jewish population, probably quite a large one, dating back to the exile of northern Israel in 722 B.C. Nisibis, which was on the Mygdonius River, an affluent of the Khabur, lay at the center of the localities mentioned in II Kings 17:6 and 18:11, where the northern tribes were deported. It was a center for the collection of temple offerings contributed in the upper Mesopotamian valley, like Nehardea in Babylonia to the south. A temple official, Judan ben Bather, lived there before 70 and was probably responsible for the transfer of funds. Neusner, 1964
When Romans invaded in 114-117, 161-165, and 193-199, Adiabene was always a center of fighting but remained loyal to Parthians. Until the 10th century, Erbil was populated by Hadhabani (Adiabeni) Kurds who gradually relocated. Salahaddin was a Hadhabani Kurd.