Took awhile to crack this one, but here is the solution in outline:
Once the West had been united under the Julio-Claudian/Herodian super-dynasty, it wasn't long before the ruling family directed their attention back to the East.
Toward the end of the reign of Herod the Great a large tribe called the Kushan began to migrate from north-west China into Bactria (Iran/Persia) and then into northern India (displacing a Scythian/Saka kingdom). From this vantage point, the Kushan dominated the Silk Route and also opened up a lucrative new Indian branch of trade. The first leader of this horde was called Heraios, evidently a pseudonym for Herod the Great or one of his sons by that name (such as Herod Philip).
Although the Kushan were from China (where they were called the Guishang or Da Yuezhi) they are considered to have been an "Indo-European" people. Their leaders used the Greek alphabet and minted coins that conformed to the contemporary Roman standard. Indian chroniclers compared the Kushan kings to earlier dynasties founded by Greeks, such as Ashoka (Antiochus II?) and then Demetrius (Demetrius II?) in the wake of Alexander the Great's invasion of India from the West. (See John Keay, India: A History, p 107-8)
Another early Kushan/Saka leader was called Jihonika (a.k.a. Jihuniasa and Jihonige). His Greek name was Zeionises, which he seems to have shared with his father/predecessor. The name Zeoionises transliterated into the otherwise unexplained Roman name Ceionius, as in Lucius Ceionius Commodus (Emperor Lucius Verus).
The name Jihonika is obviously a form of John/Johanan, a Biblical form of the god Osiris, conqueror of the East (from the West). It was Herod's design to place prince Philip in the "fifth son" (Issachar) role and place him over the Eastern portion of the Empire. When Philip could not produce a male heir, Herod grafted Philip II ("John the Baptist") onto his line. It was already deduced that Philip II was known in Parthia as Artabanus III, however it now becomes clear that the Roman Empire's influence extended much further and included what is now Pakistan and Northern India.
In the reign of Tiberius Caesar, Philip II/Artabanus III/Jihonika was subjected to a mock execution (beheading) ala Osiris. Although his eastern identity and kingship were sacrificed he later ascended to an even more powerful position as Claudius Caesar.
Claudius in turn appointed Vespatian as the next king of Parthia under the name of Vologeses. This explains the 12 year gap in the career of Vespatian (Drusus son of Germanicus) after he conquered Britain for his cousin Claudius and was named consul in 51 AD. Upon his "coming from the East" to claim the Roman throne, Vespatian appointed his son Titus as his successor both in Rome, and either Titus or Domitian as his successor in Parthia, also under the name Vologeses. The name Vologeses derived in turn from the Kushan name Kusulake (a.k.a. Kujula Kadphises), the contemporary ruler in India.
Note: There were two "Prester John" figures that came from the East and became Emperor of the West. Philip II/Claudius (“John the Baptist”)/Artabanus and then Drusus/Vespatian (“John son of Zebedee”)/Vologeses. Likewise, King John of England (Genghis Khan) was the second of two distinct Prester John figures in his own time.
Note: According to the accounting system of Josephus, Philip was the fifth son and Archelaus (Germanicus) was the sixth. In terms of Hebrew birth order Philip was the Issachar and Archelaus was the Zebulun. However, Archelaus was given the curious nickname Zebedee, which is a cross between Zebulun and Zabad (an equivalent of Issachar). In other words, the line of Archelaus was melded with that of Philip as far as the fulfillment of the Issachar role (of Eastern conquest) was concerned.
However, after the death of the first Vologeses, his son Vologeses was overthrown in the East by a prince named Pacorus II. The name Pacorus is also of Indian origin. It was the name of the prince appointed by Alexander the Great to rule India at Taxila. This earlier Pacorus was deposed by Seleucus after the death of Alexander. Another eastern king name Pacorus appeared in the 1st Century BC, and perhaps corresponds to Marcus Agrippa. This Pacorus was crown prince in Parthia under king Orodes II (Marc Antony). Like the previous Pacorus, he also lost his election and was eventually replaced by Herod the Great as king over the Eastern part of the Empire. The name Pacorus then came to represent something of a fall guy or Osiris figure in itself.
It can be deduced that the Pacorus that usurped kingship from Vologeses represents prince Herodian (son of Philip II/John/Jihonika). This Pacorus it appears also gained control over the Kushan kingdom at around the same time (80 AD) and under the name Vima Taktu (Chinese Yan-gao-zhen), who remained in power until at least 105 AD. It was from this position of strength that the line of the first John was able to recover the Roman throne after the fall of the second John (Vespatian and his Flavian successors). Nerva appointed Trajan as his successor, not because he was the best candidate in the West, but because he was a leading son of the Eastern Caesar, and this is precisely how the Kushan kings represented themselves. "Coins, plus an inscription found at Taxila, bear early testimony to the pretensions of the Kushana. 'Maharajah', 'King of Kings', 'Son of God', 'Saviour', 'Great One', 'Lord of all Lands', 'Caesar' and other such titles are reeled off as if the incumbent wished to lay claim to every source of sovereignty going." (Keay, p 111)
Note: The father of Trajan is believed to have been still living upon his succession in Rome.
Note: There is a set of names that are all anagrams of each other and all are associated with the eastern dynasty. Pacorus, Agrippa, Agbarus ("Great One", traditional king name at Edessa in Armenia), (Helio-)Gabalus, Volog(-eses), Sporakes, Priscus, and Persicus. (A further anagram, Galba, identified Emperor Galba as a former king of Armenia. Compare also Decebalus, who the only significant threat during the reign of Trajan.)
Note: Nerva would not have simply given away the Roman Empire to a collateral line. The deal would have included concessions made by Trajan for Nerva's descendants and which gave them at least a chance of recovering the throne in the generations that followed. The most likely reason for Christianity being adopted is that the line of Jesus rather than John was the one that ultimately prevailed. There was certainly a renewed emphasis on John by the Medici as reflected in Renaissance art, however this may have only been as aspect of their identification with the earlier dynasty of John. Alternately, the Medici may have been representing themselves as the neo-Jesus line and the Habsburgs as the John line to be superceded.
The Kushan Dynasty reached its peak with king Kanishka (circa 127 - 147 AD), whose reign parallels that of Mithradates IV of Parthia. The son of Mithradates IV was the long-lived Vologeses III (149 - 191 AD). In India, the contemporary ruler was Hu Vishka. Vasudeva (equivalent to the Greek name/god Heracles, see Keay, p108) succeeded in 191 AD as Vologeses IV became king in Parthia. It was also at this time that Roman Emperor Septimus Severus saw the light and married the daughter of mysterious Bassanius, High Priest of the Sun God (Helio-Gabalus). This amounted to the traditional marriage of one Emperor to the daughter of another. And it was the Eastern half of the Empire (of Bassanius) that ultimately proved more dominant than the Western, especially after the Parthian throne was replaced with one modeled after the former Persian Empire. (The question in terms of Grail lineage is whether Bassianus was a descendant of John or of Jesus. We can't yet answer that.)
Note: In this time period the most common Parthian king name ended with -aksh (as in Vologeses/Vologaksh), whereas the most common Kushan king names ended with the corresponding -ishk (as in Kanishka).
The daughter of Bassianus became mother of Emperor Caracalla. Her granddaughter later married into Roman royalty and became mother of two more emperors, Elagablus and Alexander Severus. Likewise, two Medici/Bassano princesses, Catharine and Maria, married into European royalty and became mothers of kings. However, identification with the ancient Bassianus family by the Medici served to distinguish their male line as one that held superior power in the East and was destined to dictate terms to the West, or so they had hoped. The ancient Bassianus family also provided the model for simultaneous catering to Christians, Arabs/Moors/Saracens, and Jews, and had more of a priestly status in the West rather than kingly. Likewise the Medici coveted the office of Pope in the West.
Note: The name Medici relates back to the Roman imperial title of Medicus first applied to Lucius Verus in the 2nd Century, and signified his conquest of Media (i.e., the East).
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