Jews, originally Judaean Israelite tribes from the Levant in Western Asia, migrated to Europe just before the rise of the Roman Empire. A notable early event in the history of the Jews in the Roman Empire was Pompey's conquest of the East beginning in 63 BCE though Alexandrian Jews had migrated to Rome before this event.
The pre-World War II Jewish population of Europe is estimated to have been close to 9 million. Around 6 million Jews were killed during the Holocaust, which was followed by the emigration of much of the surviving population.
The current Jewish population of Europe is estimated to be ca. 2.4 million (0.3%), composed of:
Hellenistic Judaism, originating from Alexandria, was present throughout the Roman Empire even before the Jewish–Roman wars. Large numbers lived in Greece ( including the Greek isles in the Aegean and Crete ) as early as the early part of the 3rd century BCE. The first recorded mention of Judaism in Greece dates from 300-250 Before Common Era (BCE) on the island of Rhodes. As early as the middle of the 2nd century BCE, the Jewish author of the third book of the Oracula Sibyllina, addressing the "chosen people," says: "Every land is full of thee and every sea." The most diverse witnesses, such as Strabo, Philo, Seneca, Cicero, and Josephus, all mention Jewish populations in the cities of the Mediterranean Basin. Most Jewish population centers of this period were however still in the East (Iudaea and Syria) and in Egypt (Alexandria was by far the most important of the Jewish communities, the Jews in Philo's time were inhabiting two of the five sections of the city). Nevertheless, a Jewish community is recorded to have existed in Rome at least since the 1st century BCE. (Although they may even have established a community there as early as the second century BCE, for in the year 139 BCE the pretor Hispanus issued a decree expelling all Jews who were not Italian citizens). At the commencement of the reign of Caesar Augustus (27 BCE) there were over 7,000 Jews in Rome: this is the number that escorted the envoys who came to demand the deposition of Archelaus. The Jewish historian Josephus confirms that as early as 90 CE there was already a Jewish diaspora living in Europe, made-up of the two tribes, Judah and Benjamin. Thus, he writes in his Antiquities: “ …there are but two tribes in Asia (Turkey) and Europe subject to the Romans, while the ten tribes are beyond Euphrates till now and are an immense multitude.”