16 The paternal concern of the popes for the Slavic people did not stop with the death of Cyril and Methodius. Rather, it has always shone forth in preserving among them the holiness of religion and public prosperity. In fact, Nicholas I sent priests from Rome to the Bulgarians to educate the people, and he also sent the bishops of Populonia and Ostia to govern the new Christian community. He gave a loving response in the frequent controversies of the Bulgarians concerning holy law. In this matter, even those who do not favor the Roman Church praise and admire its prudence. After this calamitous disagreement, We must praise Innocent III for reconciling the Bulgarians with the Catholic Church, and We must praise Gregory IX, Innocent IV, Nicholas IV, and Eugene IV for preserving them in reconciled grace. Similarly the love of Our predecessors shines forth in their contacts with the Bosnians and Erzevovinenses, who were deceived by evil opinions. We make special note of Innocent III and Innocent IV, who eradicated this spiritual error, and of Gregory IX, Clement VI, and Pius II who were eager to establish firmly the levels of sacred authority in those areas. Innocent III, Nicholas IV, Benedict XI, and Clement V conferred neither the last nor the least of their cares on the Serbs, who cunningly prepared deceptions to harm religion, deceptions which the popes prudently contained. The Dalmatians and the Liburnians received singular favor because of the constancy of their faith and their changing duties. John X, Gregory VII, Gregory IX, and Urban IV held them up as examples for all. Finally, there are many evidences of the good will of Gregory IX and Clement XIV toward the church of Sirmium, which was destroyed in the sixth century by barbarians and later rebuilt through the care of St. Stephen I, king of Hungary. Papal Decree
Source: Grande Munus (Vatican.va)