Pope Eugene IV (1431–1447) was one of the most significant leaders of the Roman Catholic Church, remembered in ecclesiastical history as a great reformer. He is also known for his role as the presiding figure at the Council of Ferrara-Florence. The Council began in 1438 and lasted until 1439 for the Orthodox Church, while for the Roman Catholic Church, it continued until 1445. For Roman Catholics, this Council is considered the 17th Ecumenical Council, whereas the Orthodox Church rejected it in 1443 at the Council of Orthodox Patriarchs in Jerusalem, and later confirmed this rejection at a synodal decision in Constantinople in 1472.
Even before the Council of Ferrara, in 1432, Pope Eugene IV decided to send one of the most zealous Catholic missionaries of his time, Franciscan Jacob of Marchia, to the Balkans, particularly among the Orthodox Serbs and Bogomils, for the purpose of spreading the “true faith.” Jacob of Marchia was regarded as an exceptionally educated Franciscan monk, holding a doctorate in civil law and theology, and having studied under Bernardino of Siena (1380–1444), who was later canonized as a Catholic saint. Jacob of Marchia left behind a book titled “Dialogus contra manicheos in Bosnia” (Dialogue Against the Manicheans-Bogomils in Bosnia).
A study on the Franciscans in Bosnia states the following:
“With the ascension of Eugene IV to the papal throne (1431), the supreme authority of the Catholic Church was assumed by a man who devoted his pastoral work and attention to resolving church disputes everywhere, especially in Bosnia, for which he gained significant merits. In the very first year of his reign, he allowed Franciscans Fra Ivan Cerethy and Fra Blaž Slavonac to establish three monasteries near the Dinaric Alps, as well as in Dalmatia, Bosnia, and Croatia, where Christian communities were left without priests due to Turkish invasions. The same pope then took care of appointing priests and teachers in these lands. When he opened the Council of Basel on July 23, one of the first issues addressed was the reconciliation of schismatic regions, including Bosnia.”
Before arriving in the Balkans, Jacob of Marchia had already carried out missionary activities aimed at spreading Catholicism across Italy, France, Denmark, and even Sweden. His missionary efforts in the Balkans extended across Dalmatia, Bosnia and Herzegovina, Slavonia, Srem, Bačka, and as far as Hungary. He was officially sent to Bosnia in 1432 by the Papal Council as an Inquisitor. One Catholic source states:
“To put an end to these abuses, a man of great piety and wisdom, well-acquainted with these lands, was sent—Fra Jacob of Marchia, who at that time was engaged in preaching in Hungary. By a papal letter dated April 1, 1432, he was ordered to travel to Bosnia, rectify what needed to be corrected, and restore monastic discipline where it had weakened. He was given the title of papal commissioner and vicar, along with extensive powers. Upon his arrival in Bosnia, Fra Jacob found monastic discipline in decline in certain places, and in the region of Jajce, he saw Franciscans scattered among secular households, living on private estates.”
Since the time of Pope Boniface IX (1389–1404), Franciscans had been coming to Bosnia to carry out missionary activities, often using harsh means. One historical record states:
“Pope Boniface IX, desiring to see the Hungarian crown on the head of Ladislaus, King of Naples, sent his legate, Cardinal Angelo of St. Lawrence, to Hungary to persuade the nobility and clergy. On his way, he instructed him to uproot heresies and eradicate abuses in Bosnia and neighbouring regions.”
The missionary work of the Franciscans continued under subsequent popes, as recorded in Catholic historical accounts:
“The Franciscans intensified their efforts. Fra Ivan Armandi and Fra Petruccio of Perugia travelled as missionaries across various Eastern regions. On their return to Italy, they also visited Bosnia, where they assessed the state of the vicariate and religious needs. They later went to Rome to inform Pope John XXIII in detail about everything they had observed.”
Thus, Pope Eugene IV’s initiatives, particularly through his missionary work in the Balkans and the Council of Ferrara-Florence, marked one of the most significant attempts to convert Orthodox Serbs and other Christian groups in the region to Catholicism. His methods, including the use of Franciscan missionaries, theological debates, and political influence, were part of a broader papal strategy aimed at expanding Catholic influence in Eastern Europe during a period of great religious and political transformation.
Thanks to the proselytizing efforts of Bishop Thomas of Hvar in Bosnia, King Stefan Tomaš Ostojić Kotromanić (†1461), ruler of Serbia, Bosnia, the Coastlands, Hum, Donji Kraji, Usora, Soli, Podrinje, and the Western Regions, converted to Roman Catholicism. As one Catholic source describes:
“As soon as he ascended the Bosnian throne, Stefan Tomaš was approached by papal envoy Thomas, who, through the mediation of Bosnian Franciscans, influenced him with his erudition and reputation, ultimately winning him over to the Catholic faith. Having abandoned the Patarene sect, he wholeheartedly embraced Catholicism, becoming its powerful protector and fervent promoter.”
Bishop Thomas of Hvar was appointed by Pope Eugene IV specifically for missionary work in Bosnia, as one study explains:
“Toma Tomasini was a Dominican, likely known for his theological education, affiliated with the Dominican monastery San Giovanni e Paolo in Venice. Immediately after being appointed Bishop of Hvar, Pope Eugene IV named him in 1439 as an apostolic legate in Bosnia, tasked with suppressing local heresies during the reign of King Stefan Tvrtko II.”
The Serbian king Stefan Tomaš, facing external military threats from the Ottoman Turks, as well as seeking papal approval to annul his first marriage and contract a new one, requested Pope Eugene IV’s assistance. In response, the pope swiftly granted his request:
“Eugene promptly responded to both requests in his letters dated June 29, 1445, finding it necessary to legitimize Tomaš’s position on the throne. Bogomil marriage was not even considered valid, since it was contracted under the condition of ‘if the wife was good and faithful.’ The king then married Catherine, daughter of Stefan Vukčić, the Grand Duke of Bosnia and ruler of Hum, thereby securing both a prestigious marital alliance and his conversion to Catholicism along with the Bosnian crown.”
Thus, out of fear of the Ottoman conquerors and personal desires, King Stefan Tomaš Ostojić Kotromanić abandoned Orthodox Christianity and embraced Catholicism, with the full support and blessing of Pope Eugene IV. His conversion facilitated the expansion of Franciscan missionary activity in the region:
“With such powerful backing, the Franciscans intensified their missionary work, striving to restore Bosnia’s original Catholic character, while the Holy See took special interest in both Tomaš’s political position and his ecclesiastical policies.”
The Bosnian Franciscan Vicariate: A Centre of Catholic Expansion
At that time, the Bosnian Franciscan Vicariate (founded in 1340) was already active in the region. It was divided into seven custodies (districts):
- Duvanjska (Duvno)
- Grebenska
- Bosanska (Bosnia Proper)
- Usorska (Usora)
- Mačvanska (Mačva)
- Bugarska (Bulgaria)
- Kovinjska (Kovin)
This vicariate remained active until 1463, when the Ottoman conquest of Bosnia altered the political and religious landscape. By 1514, it was divided into two vicariates:
- Vicariate Bosnia-Srebrena
- Vicariate Bosnia-Croatia
In 1517, these vicariates were elevated to the status of provinces within the Franciscan Observant Order (Ordo Fratrum Minorum Observantium, OFM Obs). From that time until today, it has continued under the name:
- “Franciscan Province of the Holy Cross – Bosnia Srebrena.”
Franciscan Proselytism Expands into Srem
Friar Jacob of Marchia continued his missionary work among Orthodox Serbs in Srem, where it is recorded:
“By 1437, it was well known that Serbs were the majority population in large parts of Srem. That very year, Pope Eugene IV sent Jacob of Marchia as an Inquisitor to spread the true Catholic faith. He successfully completed his mission, and in the following year, 1438, he focused his efforts on Fruška Gora, particularly around Kamenica and Beočin, where a significant Serbian population resided at the time.”
The Franciscan sources themselves confirm his success:
*”From what has been stated, we can conclude that Fra Jacob did not limit himself to internal affairs of his order. Instead, he actively engaged in converting heretics—which led to resistance, ultimately forcing him to withdraw from Bosnia. He was encouraged in this effort by Bishop Joseph of Bosnia, who had administered the Bosnian Diocese since 1428. Even King *Sigismund (1435), a great admirer of our saint, praised Bishop Joseph for his support of Fra Jacob’s mission. It was mainly through Joseph’s pleas that Jacob returned to Bosnia in 1487.”
Key Supporters and Papal Backing
Friar Nicholas of Trogir was Jacob’s main assistant in this missionary work:
“Following papal instructions, Fra Jacob was accompanied by an experienced and competent friar, Nicholas of Trogir. Together, they devoted themselves to strengthening the Catholic community.”
Under Pope Eugene IV’s blessing and financial support, these Franciscan missionaries expanded their activities even further:
“To facilitate their efforts, they obtained papal permission (October 4, 1437) to establish seven new monasteries in Hungary, replacing sixteen previous ones. Pope Eugene IV then granted additional privileges, authorizing Fra Jacob (December 7, 1437) to absolve sins usually reserved for bishops, since it was difficult and costly for believers to reach a bishop for confession.”
Franciscan Engagement in Religious Debates
Fra Jacob actively debated Orthodox clergy:
“Never neglecting his preaching, Fra Jacob authored a Latin treatise against the Bosnian Patarenes, equipping his fellow Franciscans with arguments against heresies and reinforcing Catholic doctrine.”
Their missionary efforts spread across all territories where Orthodox Serbs lived:
“The following year, we find Fra Jacob across the Sava River, likely because Hungarian and Croatian bishops urged him to continue preaching and eradicating heresies, which had severely disrupted religious and social stability.”
Papal Approval and Expansion of the Vicariate
Satisfied with the progress of the Franciscans, Pope Eugene IV expressed his appreciation but also warned about the spread of Hussite teachings:
“In a letter dated January 23, Pope Eugene IV praised the Bosnian Franciscans, stating that they had become a bulwark of faith and had devoted themselves to eradicating heresies. He granted Fra Fabian Bačanin, the Bosnian vicar, and his successors the authority to act as inquisitors throughout the entire Bosnian vicariate, even if local bishops refused to cooperate. The Pope specifically ordered them to combat Hussites and sorcerers and threatened excommunication to any who resisted, while granting indulgences to those who supported the Franciscans.”
Recognizing the strategic importance of the Bosnian Vicariate, Pope Eugene IV expanded its jurisdiction, as seen in his decree:
“On January 29, 1445, Pope Eugene issued another apostolic decree, adding all Franciscan monasteries in Wallachia, Moldavia, Transylvania, Budapest, and Szeged to the Bosnian Vicariate, and granting Cardinal Julian, the papal envoy, the authority to assign additional monasteries.”
Conclusion: The Expansion of Catholic Influence
Encouraged by papal support, Bosnian Franciscans intensified their missionary work:
“With such success and papal favour, the Franciscans continued their pastoral duties with renewed zeal. Seeing that King Stefan Tomaš tolerated the Bogomils and showed them undue respect, they openly criticized him, refusing to recognize him as a true Catholic.”
This historical process illustrates how papal authority and Franciscan missionaries played a decisive role in spreading Catholic influence among the Serbs of Bosnia and Srem during the 15th century.
The Continuation of Franciscan Proselytism under Papal Blessing
This priestly boldness shown by the Franciscans did not alienate King Stefan Tomaš from them—rather, it amazed him, leading him to send a special envoy to inform Pope Eugene IV of the situation. The king even requested permission to maintain relations with the Bogomils, to show them outward respect, and at the same time continue receiving the Holy Sacraments, while waiting for the right moment to eradicate them completely.
Papal Directives: Ensuring the Sacraments for the King
The king’s loyalty to Pope Eugene IV was evident in the papal decree ordering the Franciscans to continue administering the Sacraments to him, despite his political ties to the Bogomils:
“At the same time, the king declared that he had been raised in the Christian faith from childhood but that heretics were in the vast majority in his realm, making it impossible for him to openly declare himself as their opponent. Pope Eugene took the king’s reasons into consideration and, in a letter dated November 11, 1443, instructed his envoy Thomas to order the Franciscans—‘the only Catholic priests in Bosnia’—to administer the Sacraments to the king as often as he requested, provided that he was otherwise a good Catholic and his dealings with heretics were merely a matter of diplomacy.”
Thanks to the king’s devotion to Pope Eugene IV, Franciscan proselytism continued to expand across the Bosnian Vicariate:
“After a brief misunderstanding between the king and the Franciscans, a deep mutual respect and cooperation developed. The following year, the king asked the Pope for permission to have two Franciscans serve as chaplains for himself and the queen, and to be able to employ them on diplomatic missions without needing additional approval from their monastic superiors. Eugene granted this request on June 18, further strengthening the Franciscan influence at the royal court. The presence of these court priests played a crucial role in solidifying the king’s Catholic identity, which he publicly displayed by building new churches and acquiring church vestments.”
The Expansion of Roman Catholicism Brings Papal Joy
The spread of Catholicism among the Slavic peoples—not just in Bosnia but across other territories—brought great joy to Pope Eugene IV, as documented by the Franciscans themselves:
“What must particularly delight Catholics at this time is that the widely extended Bosnian Vicariate achieved remarkable success among other Slavic peoples as well, especially among the Rusyns in Hungary and Transylvania. In this letter, the Pope first praises the skill and dedication of the Franciscans, attributing the conversion of many Rusyns to the monastic way of life and the fruitful preaching of the Bosnian brethren. The Pope also acknowledges the desire of the newly converted and their priests to remain under the spiritual guidance of their Franciscan missionaries, especially if there were no native Catholic clergy available.”
Moreover, Pope Eugene granted additional privileges to the Franciscans:
“He granted them permission to build churches, bell towers, and houses from the Adriatic Sea all the way to the Tatar border (likely the Prut River)—meaning, across the entire Bosnian Vicariate. He authorized them to celebrate divine services, enroll new members into the Third Order, accept new monasteries under their jurisdiction, conduct burials within their churches, and forbid secular clergy from interfering in their missionary work. Any attempts to obstruct them were to be punished by papal decree and the Bosnian vicar’s authority.”
Franciscan Proselytism Spreads Beyond Bosnia
Under Pope Eugene IV’s blessing, the Franciscans expanded their proselytizing mission across the entire Balkans, targeting not only Orthodox Serbs but also other Orthodox Slavic peoples:
“The zeal of the Bosnian Franciscans knew no political boundaries, as they tirelessly spread the light of truth and expanded the Church’s reach across new lands.”
The Death of Pope Eugene IV and the End of His Missionary Campaign
The aggressive missionary campaign initiated by Pope Eugene IV, which assigned Bosnia’s Franciscan Vicariate and Italian Franciscans (such as Friar Jacob of Marchia, Bishop Thomas of Hvar, and others) to convert Orthodox Serbs and other Slavs, was abruptly interrupted by his death on February 23, 1447.
Pope Eugene IV and the Catholicization of the Slavs
From all the evidence presented so far, we can conclude that the main goal of Pope Eugene IV, as well as all subsequent Roman pontiffs, was singular: the Catholicization and unification of all Slavic nations, including the Serbian people, under the faith of the Roman Church and the authority of the Pope. This is explicitly confirmed by Franciscan sources themselves:
“Among the many efforts undertaken, Eugene was particularly dedicated to reconciling the South Slavic regions with the Mother Church and binding them to the West, for just as all Christian rulers were united by the same needs and interests, so too should they be united by the same religious convictions, thereby creating an impenetrable barrier against the enemies of the Cross of Jesus.” [29]
Thus, the Franciscan missions in Bosnia and other Serbian lands, under Pope Eugene IV’s direct supervision, were not an isolated endeavor but a well-coordinated effort aimed at subjugating Orthodox Christian lands to the authority of Rome. This process was carried out through systematic missionary activities, the establishment of monastic communities, direct political pressure on rulers, and financial and spiritual support for Catholic converts.
Despite these efforts, the Serbian Orthodox faith remained resilient, and the Franciscan influence, though strong at times, never fully succeeded in assimilating the Serbian people into Roman Catholicism.
Author: Doctoral Candidate, National and Kapodistrian University of Athens
