"At first the Roman state did not distinguish between Jews and Christians. In fact, we may be sure that the Romans simply saw Christians as a group of Jews, or a group within the Jewish community. So when the Jews were expelled from Rome in the time of Claudius, we may be sure the expulsion included both Jews as well as Christians.” Shaye D. Cohen, Ph.D., Brown University
According to Suetonius, a Roman historian who wrote during the second century, this expulsion of the Jews from Rome took place in 49 AD. It seems that there was a significant population of Jews in Rome. Unrest and riots within that community prompted the emperor Claudius to banish all Jews from the city.
Christians living within the Jewish community were forced to leave as well. To Claudius and the other Romans, they looked like Jews. In one way, this close identity with the Jews was an advantage for Christians: Judaism was still a legal religion within the empire, while Christianity itself had no legal standing. On the other hand, when the Jews fell out of favor with the Romans, the Christians suffered the same fate.