He was crowned by the nobles in place of his deposed and blinded uncle Balash (484–488).
At this time the empire was utterly disorganized by the invasion of the Ephthalites or White Huns from the east. After one of their victories against Peroz I, Kavadh I had been a hostage among them for two years, pending the payment of a heavy ransom. In 484 Peroz I had been defeated and slain with his whole army. Balash was not able to restore the royal authority. The hopes of the magnates and high priests that Kavadh I would suit their purpose were soon disappointed.
Kavadh I gave his support to the communistic sect founded by Mazdak, son of Bamdad, who demanded that the rich should divide their wives and their wealth with the poor. His intention evidently was, by adopting the doctrine of the Mazdakites, to break the influence of the magnates. But in 496 he was deposed and incarcerated in the "Castle of Oblivion (Lethe)" in Susiana, and his brother Djamasp (496–498) was raised to the throne.
Kavadh I, however, escaped and found refuge with the Ephthalites, whose King gave him his daughter in marriage and aided him to return to Persia. In 498 Kavadh I became King again and punished his opponents. He had to pay a tribute to the Ephthalites and applied for subsidies to Rome, which had before supported the Persians. But now the Emperor Anastasius I (491–518) refused subsidies, expecting that the two rival powers of the East would exhaust one another in war. At the same time he intervened in the affairs of the Persian part of Armenia.
So Kavadh I joined the Ephthalites and began war against the Romans. In 502 he took Theodosiopolis (Erzurum) in Armenia; in 503 Amida (Diarbekr) on the Tigris. In 505 an invasion of Armenia by the western Huns from the Caucasus led to an armistice, during which the Romans paid subsidies to the Persians for the maintenance of the fortifications on the Caucasus.
When Justin I (518–527) came to the throne in Constantinople, the conflict began anew. The Persian vassal, Mondhir of Hira, laid waste Mesopotamia and slaughtered the monks and nuns. In 531 Belisarius was defeated at the Battle of Callinicum. Shortly afterwards Kavadh I died, at the age of eighty-two, in September 531. During his last years his favourite son Khosrau I had had great influence over him and had been proclaimed successor. He also induced Kavadh I to break with the Mazdakites, whose doctrine had spread widely and caused great social confusion throughout Persia.
In 529 they were refuted in a theological discussion held before the throne of the King by the orthodox Magians, and were slaughtered and persecuted everywhere; Mazdak himself was hanged. Kavadh I evidently was, as Procopius (Pers. i.6) calls him, an unusually clear-sighted and energetic ruler. Although he could not free himself from the yoke of the Ephthalites, he succeeded in restoring order in the interior and fought with success against the Romans. He built some towns which were named after him, and began to regulate the taxation.
