On August 13, 339, C.E., Emperor Constantius II enacted a series of new laws restricting the freedom of Jews in the Roman Empire even more than under the anti-Jewish legislation imposed by his father, Constantine the Great.
It was under Constantine (who ruled 306-337) that Jews were prohibited from taking action, particularly violent action, against Jews who had converted to the rapidly growing Christianity. A law enacted in 315 C.E. imposed death on any Jew who so harassed a Christian proselyte. Similarly, any non-Jew who decided to convert to Judaism also risked execution.
On Constantine’s death, his three sons, Constantine II, Constantius II and Constans, divided up control of the empire between themselves. Constantius was left in charge of the east, including Asia Minor, Palestine and Egypt. Quickly, the arrangement descended into internecine fighting, at the end of which, in 350, Constantius remained the empire's sole leader.
It was in 339 that Constantius, at the time still emperor of the East, wrote a letter to one Euagrius, whom some historians have identified as “Praetorian prefect” -- a high administrative official – of the region, outlining the new regulations.
They were three in number: First, Jews were now prohibited from owning Christian slaves, and any such slaves that were in Jewish possession at the time of the law’s enactment would automatically be transferred to ownership of the imperial treasury (rather than being freed).
Second, any Jew who had owned a slave and, in the case of a male, had him circumcised, was to lose the slave and also be executed, presumably in that order. Finally, Jews were specifically prohibited from marrying Christian women who had been working in imperial weaving factories (called gynaeceum). Any such marriages were to be dissolved.
Probably the prohibition on ownership of Christian slaves was the most onerous of these new rules, and one with not just religious implications, but also real economic ones.
Jewish-owned businesses were in competition with state-owned ones, and the holding of slaves was integral to running a profitable business. Being denied the right to hold non-Jewish slaves, at a time when both Jews and pagans were taking on Christianity in large numbers, put Jewish entrepreneurs at a disadvantage.
The same explanation presumably applies to the rule specifically denying Jewish men the privilege of marrying Christian women previously employed in state-owned textile factories.
In 351, when Constantius was preoccupied with political intrigues in the west, he appointed his cousin Constantius Gallus to be Caesar of the east. It was in this context that a revolt among the Jews of the Land of Israel took place, in protest of the persecution that they were suffering at the hands of the imperial government and of Christians in general. Gallus sent the general Ursicinus to put down the revolt, which he did with great brutality.
Gallus himself was put to death by Constantius in 354. His brother, Julian, succeeded Constantius as emperor when the latter died, in 361. It was Julian who declared his readiness to have the Jews return to Jerusalem and rebuild the Temple, a plan that never materialized, both because of Julian’s early death and because of a devastating earthquake in Palestine in 363.