In January 1444, Pope Eugenius IV (r. 1431–1447) trumpeted to the Christian princes his recent string of successes in bringing Eastern Christians into the Catholic fold. Having secured Church union with the Greeks at the Coun- cil of Florence in 1439, the Armenians, Jacobites, Maronites, Ethiopians, and Bosnians all followed suit, sending their envoys and submitting to the pope. Eugenius called on the Christian princes to support the crusader army led by the Polish and Hungarian king Władysław (r. 1434–1444) and papal legate Giuliano Cesarini. This army was supposed to drive the Turks from Europe, save Con- stantinople, and ensure the unity of all Christians under the wing of the Roman Church. 1 The expedition, as is well known, ended in a catastrophic defeat at the Battle of Varna in November 1444, but the papal project moved forward. By pursuing crusades against the Ottomans and securing recognition from the Eastern Christians, Eugenius and his successors sought, in fact, to reclaim their spiritual and political authority over all of Christendom. 2 There were, however, two sides to that coin. Eastern Christians faced a prob- lem: to receive help, they had to admit the errors of their traditions and accept the tenets of the Catholic faith and the primacy of the Roman Church. The pressure exerted by the papacy on the Greeks to accept the Union of Florence and the rifts this caused within the Greek communities are well studied. 3 The popes, however, put no less pressure on the Bosnian kings. The confessional dynamics that the pa- pacy faced in this kingdom, situated at the contact zone of Catholic and Orthodox Slavdom, was far more complicated than the one in the Greek lands. Next to the dominance of the Catholics in the western and northernmost parts of the kingdom, and that of the Orthodox in the southeast, Bosnia’s heartland was predominantly populated by the believers of the Bosnian Church, an autocephalous Christian church that had long wielded dominant infuence over both the Bosnian court and society at large. Though the members of the Bosnian Church called themselves Krstjani (Christians, sing. Krstjan ), the popes considered them dualist “Manichean heretics.” Eugenius thus may have framed his efforts to Catholicize Bosnia as part of his uniate programme of bringing the Eastern Christians under the papal wing, but there was no common ground with the Krstjani for talks over fner theological points. He and his successors sought to destroy them root and branch. 9 The Renaissance papacy and Catholicization of the “Manichean Heretics” Rethinking the 1459 purge of the Bosnian kingdom Luka Špoljari ć