Pope Pius II (1458-1464) in his work "Cosmografia" wrote while describing the Adriatic countries: "Behind Albania come the Illyrian people towards the west and north. This people were called the Slaves in our time and they call themselves Bosniaks, other Dalmatians, third Croats, Istrians and Carniolans".Bosnia - land of the Bogomils
The first mention of heresy in Bosnia stems from the first half of the 10th
century. In the letter of Pope Ivan X, sent to an archbishop from Split and the local clergy in 925, a complaint is mentioned that in the neighbouring diocese or land (referring to Bosnia), there is a science "located in holly books". The Pope rebukes them for not paying attention and "tacitly approving it". Though here there is no direct mention of who the heretics were, nor is there mention of the character of their teachings, but there is mention that it is not "in the holly books", this clearly implies that the Pope saw it as heresy. That it refers to Bosnia and its heretics is quite clear since in the later period Bosnia was the only country in this part of Europe where heresy developed and where it, so to speak, gained the status of state religion. (Source: F. Šišić, Manual on Croatian history, I/1 Zagreb 1914., p.215.)
Another important document confirms that the Bogomils were present in Bosnia in the 10th
Canterburyjski (San Anselmo) from Alexandria in Italy, which lived and worked in the 13th century, in one of his documents mentions that "the heretics were initially in Bosnia from where they spread their teachings to Lombardy, and from there towards France, from where it arrived to Orleans in 1022 and into Arras in 1025." (Source: A. Dondaine, Le Tractatus de hereticis d'Alexandrie, Arch. Fr. Praedic, XX, Rome 1950., p. 308-324).Letter of the Roman Pope Gregory IX about Bosnia as a nest of heretics
"In his letters from 1232 to 1239 (pope Gregory IX) mentions heretics in Bosnia several times. Thus on May 30th
1233 he wrote to the cardinal Jakov Prenestinsky his legate in Bosnia, that with sorrow he discerned from his report, that the Bosnian bishop fell "into the bitterness of the crazy heresy ". That's why he ordered to place two, three or four bishops?! (though he has no support in Bosnia).
About the Bosniaks he says: "About the inhabitants of that country he says, that they are poor in estate, and rich in wickedness, since in most part they are infected with wickedness of heresy". (Pope doesn't hide his hatred towards the Bosniaks and confirms that Bosnia is mostly heretic but despite that he plans to place bishops in Bosnia?!)
In the second letter from February 13th
1234 Gregory IX wrote: "such is the multitude of infidels in Bosnia and surrounding areas, that the entire country (Bosnia) weeps and aches, barren and impassable". On August 8th
1236 the pope wrote to Sibislav, the duke of Usora, son of the former king of Bosnia Stephen (Stepan Kulinić), that "he received with joy the news that he is among the dukes of the Bosnian diocese?! (which never existed), which are infected by the taint of heretic wickedness, like a lily among thorns".
From this letter one can clearly conclude that the pope clearly wrote to one catholic among the Bosnian nobility, commending him for not falling into heresy like all the other Bosnian nobility. He mentions that in the letters, which he wrote to Ancila, the mother of Sibislav and to Hungarian bishops (since there are no Bosnian bishops), to whom he recommends Sibislav and his mother". (Source: Dominik Mandić "Bosnia and Herzegovina volume II: Bogomil church of Bosnian Christians" p. 33-34).Letter of Pope Ivan XII 1319 to Croatian liege Mladin Šubić
"They are learning disastrous heretical fallacies. Every believer has to stand up against such people and destroy them in order to up root their poisonous anger to prevent contamination of other believers. We often, with great sorrow, listened, from credible sources, that the land of the Bosniaks is the home to heretics, that churches are being abandoned, the clergy has been up rooted, Christian sanctities are being trudged on, the cross is not being respected, moreover, there is no sacrament of christening".Bosniaks - dualists
"Dialogus contra manichaeos in Bosna" translated "Dialogue against Manichaeism in Bosnia" is the work of Jakob de Marchia who was placed as the vicar of Bosnia and main inquisitor by the Roman curia. This work which was written on the ground of Bosnia describes the Bosniaks as Manichaeists and as bi-fundamental heretics (dualists). In the dialogue it is mentioned that they baptize themselves with the book, and not water, similarly to the western Cathars, which is the original spiritual, dualistic baptism called consolamentum.
The work "Dialogus contra manichaeos in Bosnia" was in the hands of church censors in 1697 when the issue was canonization of Jakov (Jakob) Markijski (de Marchia). Since then the work has been lost. Censors Johannes Bapt. Lucini and Jochannes Bapt. Barberio exhausted the content of the work and incorporated it into their analysis which is contained in a collective work called "Monumenta canonizationis B. Jacobi de Marchia" which is in Rome.
Jakob de Marchia who was labelled a saint was a doctor of canonical law and a great fighter against heresy. Senate of Dubrovnik called him "the most elegant sower of the Lords word". His lack of success in converting Bosnian Patarens he justified to the pope by claiming that he lacked support from the royal couple Tvrtko II and Dorothea. Dorothea and Tvrtko became very unpopular among the Franciscans, which called Dorothea an "evil woman".They would rather die than accept orthodoxy
One of the four grand inquisitors which were labelled saints by the Roman church is inquisitor Capistran (Giovanni de Capistrano) which was also known as the expert on heresy. In his letter to pope Kalisto III 4/7/1455 wrote: "Bosnian Christians are not members of the Eastern church, nay they would rather die in disbelief, than accept the religion of the Rašan (Serbs)." (Ref: Franjo Šanjek Phenomenon "krstjani (Christians)" in medieval Bosnia and Hum, collection of works.)
How much hatred and revolt there was against the Pope, and the eastern church - which at one moment had a competition who will commit greater genocide over the Bogomils - is best confirmed by this letter according to which the Bogomils inclined towards the Ottomans as protectors against Christian evil (inquisition) and murdering.
At the end of 1456 pope's legate Ivan Karahal sent Nikola Barbucini to king Tomaš in order to talk him into declaring war against the Ottomans in unison with Hungary. After the stay and discussion with the Bosnian king, Barbucini sent a report to the pope's. legate that Tomaš is willing to go to war against the Ottomans but that "he can't because of the Manichaeists which are still a majority in Bosnia, and which love the Ottomans more than the Christians..". The statement that the Bosnian king gave to Barbuicini was repeated literally, three years later in 1459 in his letter to pope Pius II.