Per Isaac Asimov in The Dark Ages, European antisemitism began in earnest with the Visigoths as a result of post-Arian conversion politics on the Iberian peninsula.
The extremism they developed remained a Spanish heritage right down into modern times.
Religious tolerance, once established, was usually extended to Jewish people, as well.
Visigothic kings initiated a policy of brutal antisemitism, which has stained Christian Europe ever since.
