After his legions crushed the Jewish Revolt in 70 CE, Titus—son and heir of then-Emperor Vespasian—took as his consort Berenice, whose brother, Agrippa II, had been the last king of Judea. (Since the Judean royal family had opposed the rebellion, Titus’ choice might have been a gesture of reconciliation with local loyalists.) Frederic Brandfon notes that many Romans reacted with fear that Berenice would persuade Titus to become a Jew, or that their children would be raised as Jews, and they might find themselves with a Jewish emperor:
Indeed, preceding dynasties had also faced the charge of Judaizing the empire. Emperor Claudius, who preceded Titus by fewer than twenty years, had a visiting dignitary, Isidorus of Alexandria, executed for accusing him of being Jewish. A few years later, Nero, who ruled Rome until 68 CE . . . could not escape association with Jews. His wife was a “God-Fearer,” that is. a person who engaged in some Jewish practices without converting. There was precedent, therefore, for both Titus’s romantic entanglement and the accusations that came with it
Titus understood that Berenice’s potential ascendance to imperial power was a threat, real or imagined, to the future of the nascent Flavian dynasty [founded by his father], which, like all dynasties, needed stability and not controversy. Berenice was forced into exile. . . . The notion that a single Jew could transform Western society into a Jewish empire was a fear that did not die.
Even the actual transformation of the Roman empire through the establishment of Christianity as the state religion—a faith that incorporated the Jewish Bible, and replaced traditional Roman Gods with a crucified Jew—did not bring an end to the charge of Judaizing: later emperors were accused of being Jewish when they took the side of Jews against Christians. In 387 and 388, synagogues were burned in both Rome and Callinicum in Mesopotamia. The Western emperor Magnus Maximus ordered the Roman synagogue rebuilt, and was promptly labeled a Jew.
As Brandfon goes on to demonstrate, strikingly similar fears persisted in Rome itself into modern times.
Read more on Tablet: https://www.tabletmag.com/jewish-arts-and-culture/296616/berenice-rome-replacement-theory