Some 1900 years earlier, the Roman Empire was having problems with the inhabitants of one of their recently conquered territories resisting their authority and decided to make an example of them by expelling them from their territory. They ended up scattered all over the Empire and beyond, whilst maintaining their language, religion and customs. A few hundred years after that, Rome adopted a new religion, worshipping a guy they had put to death a few hundred years earlier in that particular territory, and had to find someone else to blame, and the people they expelled were the most expedient candidate. And so, we had a millennium or two of European Christianity very unsubtly stating that the Jews were the killers of Christ, which got embellished, as urban legends do, with a number of other equally lurid myths about them poisoning wells with the Plague and abducting Christian babies for their blood. People generally (with exceptions) stopped believing in those myths, but the underlying attitudes of suspicion remained ingrained in culture.