Sermons preached in medieval Christian churches and public places were often a vehicle for the expression of the most virulent anti-Jewish sentiments. The texts of these sermons look very much like other theological treatises when they are bound together in someone's collected writings, but the difference in genre is significant. Unlike the treatise, which was (until the sixteenth century) expensive to reproduce and accessible only to individuals in isolation, the sermon could reach a multitude of listeners simultaneously. With its power to excite the emotions enhanced by a charismatic delivery, it could appeal to the psychology of the crowd for immediate action. While the best-known anti-Jewish sermons of antiquity by Melito of Sardis and John Chrysostom do not seem to have had direct and immediate consequences, those of popular medieval Christian preachers often did. Such figures as Berthold of Regensburg in Germany, Ferrant Martinez and Vincent Ferrer in Spain, Bernardino of Siena, John Capistrano and Bernardino da Feltre in Italy, attest to the power of the preacher to spread negative views, sometimes with devastating results.1