When the Spanish Monarchs decided on the expulsion of Muslims from their territories of Castile (1502) and Valencia-Catalonia-Aragon (1525), they hoped most of the Muslims would remain in Spain, accept baptism, and rapidly become “good Christians.” But if the decrees of expulsion were followed by massive conversion, the elimination of Islam was far from achieved among the Moriscos (the converts and their descendants). This situation aroused much discussion among theologians, prelates, and royal counselors about the validity of forced conversion and the best means to ensure the effective conversion of the Moriscos. In this debate historical precedents were used as models for the Spanish Monarchs or as examples of bad decisions. Thus the reminder of the forced conversion of the Jews (between 1391 and 1492) served to indirectly criticize the forced conversion of the Muslims of Valencia. The remote episode of the forced conversion of the Jews by King Sisebut in the early seventh century was also used to recommend or to condemn the forced conversions and expulsions of Muslims and Moriscos. In this way, anti-Judaism put its mark on the relations between the Catholic powers and other religious traditions, far beyond the Christian-Jewish face-off.