KAVAD (488 - 531)
There's no shortage of sources for the long and interesting reign of Kavad. Unfortunately they disagree dramatically with each other, and reconstructing the exact course of events is impossible. It's made more complicated because he was actually king twice - with a three-year (or 2- or 6-year) interval where his brother Zamasp replaced him. This page is a personal take which tries to make sense of the confusion.
Kavad's first reign (AD 488 - 496) - the young idealist
Kavad was 15 (or maybe even younger) when he became king, after the nobles had lost patience with Balash. He'd actually grown up among the Hephthalites, as he'd been given to them as a hostage after his father's second defeat, and they probably helped him to oust Balash.
He must have been supported by leading nobles, who perhaps then tried to exert too much influence over the young king, who began looking for a way to curb their power.
A gilded silver plate showing either Kavad I or his predecessor Peroz I hunting rams (Sasanian kings are identified from the design of their headgear).
Kavad seems to have got an idea of how to do this from the teachings of a Zoroastrian "protestant" sect. His ideas and theirs coincided in several respects: Kavad was a pacifist and a vegetarian. But their really revolutionary idea involved the sharing of women, an idea that was much misunderstood at the time and has been ever since. The three contemporary sources say:
Kavad reestablished the abominable heresy which teaches that "women should be in common and everyone should have intercourse with whoever he liked". [Joshua the Stylite c. AD 507]
Kavad passed a law that "Persians should have communal intercourse with their women". [Procopius c AD 527-531]
It is said that Kavad made a law according to which "women were to be available to men in common". [Agathias, died c AD 582]
Females on a silver and gilt vessel from the Sasanian period. Photo Wikimedia commons.
It appears to have been a move to undermine the power of the nobles, who were beginning to think they were stronger than the king. The nobles kept hold of their fortunes and increased them over the generations partly through endogamy (marrying within the family) - thus no money would leak outside the great families, and the rich stayed rich and the poor stayed poor. Kavad's ideas would lead to a breakdown of this traditional order of things - and the nobles would have to share their women. The mystique of the noble families, and their hereditary privilege would be ended. He does not appear, though, to have been in favour of sharing all property - as the communist followers of Zaradusht were - only women. He wasn't against marriage or the inheritance of property: he was simply in favour of preventing the wealthy from hoarding women in their harems, or keeping their daughters for themselves.
"When Adam died, God let his sons inherit the world equally; nobody has a right to more property or wives than others." [al-Tabari]
But of course, it didn't happen. There was a violent reaction, and Kavad (remember how young he was) was dethroned and put in prison, to be replaced by his brother Zamasp in AD 496.
Prison 496 - 499 (?)
Kavad was imprisoned in the notorious "Castle of Oblivion" (sounds like a computer game!), from where he escaped. He went back to the Hephthalites, who helped him to get his kingdom back. Zamasp surrendered without fuss.
Kavad's Second reign (?499 - 531)
When Kavad was reinstated, he forgot about his youthful ideas, and ruled successfully and conventionally for another thirty years. He abandoned the woman-sharing idea, made peace with the religious establishment and got rid of only those nobles who'd supported his removal from power. There were various important problems to deal with.
The Caucasus mountains: not as secure a barrier as they look.
He needed money to pay off his Hephthalite friends. The Byzantine emperor (Anastasius at this time) was supposed to help pay for their joint defence of the Caucasus, but was refusing to do so - a good excuse to attack them in search of plunder. Between AD 502 and 506 there was inconclusive fighting between the two super-powers in northern Mesopotamia: Kavad wasn't able to press home his advantage, because he also had to deal with attacks in the Caucasus. Peace was made in AD 506, and Kavad got his money. See also under Sophene
Between about 525 and 528, there was trouble with Kavad's Arab allies, the Lakhmids. An Arab tribe, the Kinda, invaded and briefly occupied their capital at Hira. A reminder that Arabia Deserta was capable of asserting itself.
Also in the 520s there was renewed confrontation with the Byzantines in the Caucasus region - there were Sasanian victories, including a defeat of the emperor Justinian's general Belisarius, but basically the stalemate continued.
In the early 530s Kavad joined his Lakhmid Arab friends in an invasion of Byzantine Syria, trying to capture Antioch - which they nearly did. But it all came to nothing when Kavad, now an old man, died in 531.
At home, Kavad had begun a survey of his kingdom, planning to produce a kind of "Domesday Book" - a complete register of all property - its ownership, location, cultivation and value - right down to who owned each individual olive tree and date palm. This was a preliminary to reforming the tax system, which Kavad probably started to implement. The grievances which tax reforms caused to the small-scale farmers began to be exploited by Mazdak - a Zoroastrian heretic, and follower of the Zaradushti sect which had inspired Kavad's woman-sharing policy during his first reign. Mazdak wanted not just women to be shared equally, but all property - he's often been called the first communist:
Mazdak's followers claimed "they were taking from the rich and giving to the poor and that whoever had a surplus of land, women or goods had no more right to them than anyone else." [al-Tabari]
It's not clear whether Mazdak's followers were a serious problem during Kavad's reign: they certainly became one later.
Kavad had three sons - and wanted the youngest, Khusrau (Chosroes in Greek and Latin) to succeed him. He'd tried to get him adopted by the Roman emperor Justin, so that he could be sponsored and protected by the Byzantines. But Justin refused. When Kavad died, the result was once again a free-for-all as brothers fought each other for the crown.
A conflicting view and full discussion can be found here - Khodadad Rezakhani: Mazdakism, Manichaeism, and Zoroastrianism: In Search of Orthodoxy and Heterodoxy in Late Antique Iran