An important and interesting phenomenon of Bosnian history are Krstyans, members of the mysterious Bosnian Church – a Christian religious sect. Krstyans are also known under the name of Good Christians (Dobri Krstyani). According to studies of fra Leon Petrovic, reports of Hungarian clergy to the Pope in 13th century about the “heresy” of Bosnian Krstyans were unfounded. The “heresy” of Bosnian Krstyans was invented by church authorities in Budim in order to subjugate Bosnia to Hungary first in ecclesiastic, and then in political sense. This policy succeeded to separate Bosnia from the Dubrovnik Archdiocese (which was also accused for “heresy”!), and to attach it to the Hungarian Archdiocese in Kalocsa in 1247. Several crusades against Bosnian “heretics” had been undertaken in the 13th century. According to recent investigations, their overall number in the 15th century was already small compared to the Catholic population in Bosnia (Turkish sources recorded only 700 Krstyans in 1468/69, see [Gavran, IV, p. 101). They all disappeared with the fall of Bosnia under Turks in 1463.
According to Franjo Sanjek, claims about massive passage of Bosnian and Herzegovinian Krstyans to Islam are historically unfounded. See his article “Dobri Muz’je” Crkve bosanskih i humskih krstjana in Stecak 58/1998, Sarajevo. See also [Sanjek]. The history of Krstyans of Bosnian Church is studied in an illuminating monograph [fra Leon Petrovic].
It is interesting that they had institutions of their own that they called hizha (house), while the bishop of the Bosnian Church was did (= grandfather), both typically Croatian names, in dialectal use even today. They were never called “hristjans” or “hrischans”, as would be the case if they were of the Serbian provenance. The institution of “did” existed also in old Croatian Kingdom, until its union with Hungary in 1102.
Another important and well documented fact regarding Krstyans in Bosnia is that liturgical books of the Bosnian Church had been transliterated from the Croatian Glagolitic sources into Croatian Cyrillic (Bosancica). Thus Krstyans are very closely related to the Croatian Glagolitic tradition.
Croatian Glagolitic sources related to Bosnia and Herzegovina (see also [Damjanovic, Glagoljica na podrucju danasnje BiH]):
- Kijevci fragment found near Kozara mountain found in NW Bosnia, 11/12th centuries, in its character very close to Glagolitic stone inscriptions in Western Slavonia (12/13th centuries) discovered in 1996,
- the Grskovic fragment of Apostle (12th century),
- the Mihanovic fragment of Apostle (12th century),
- inscription of prince Miroslav from Omis, 12th century (Croatian Cyrillic and Glagolitic),
- short Glagolitic inscription from Posusje (Grac), containing only two letters (T or V), according to Branko Fucic 12/13th centuries, see [Damjanovic, Glagoljica na tlu danasnje BiH]
- a leaf of Glagolitic parchment, known as the Split fragment (12/13th centuries), held in the treasury of the Split Cathedral, probably from Bosnia,
- Glagolitic inscription in Livno, (content: A SE PI / SA LU / KA DI / AK / 13 / 6 / 8) 1368, (and three more fragments, groblje sv. I’ve)
   
Many thanks to dr. fra Bono Vrdoljak, Livno, for this information
- Sokolska isprava, Glagolitic quickscript document from 1380, from western Bosnia (at that time part of Croatia, in Turkish time called Turkish Croatia),
- Kolunici inscription, 14/15th centuries, found near Bosanski Petrovac, with OSTOJA inscribed twice (the first one is mirror, in reverse order), see [Fucic]
- Inscription from Dragelja, south of Bosanska Gradiska, lost (there is no photo or drawing)
- Cajnice Evangelistary, 14/15th centuries, contains a part written in the Glagolitic script (St John, 17-20), and a Glagolitic alphabet (incomplete and rather deformed),
- Glagolitic inscription from Bihac (kept in Fojnica), is still studied,
- two glagolitic fragments on parchment from 14th century are today in the Franciscan Monastery Livno (Gorica)
- Glagolitic document from Ostrozac near Bihac in BiH, 1403, vellum with seal on purple silk ribbon, (kept in the archives of prices’ of Auersperg in Ljubljana in 1890’s, today probably in National Library of Ljubljana, [Lopasic, p. 294]),
- Hrvoje Glagolitic Missal, 1404 (held in Constantinople, Library of Turkish sultans Topkapi Saray),
- Venice collection (Mletacki zbornik), written in the Cyrillic, was transcribed from glagolitic original (Josip Hamm)
- Glagolitic inscription from Golubici near Bihac in western Bosnia (ie. Turkish Croatia), carved in 1440 and in 1442, mentioning knez Tomas (ie. Prince Toma Kurjakovic) from Krbava; it is held in the famous Franciscan monastery in Fojnica in central Bosnia; this is the largest glagolitic inscription found on today’s Bosnia and Herzegovina, see [Fucic, Glagoljski natpisi, p. 164];
A detail from the above Croatian Glagolitic monument from Golubici
- Glagolitic page from the Manuscript of Krstyanin Radosav, 1443 – 1461 (kept in the Library of De Propaganda Fide in Rome), transcribed into standard Croatian Glagolitic in 18th century by Matija Sovic; the book contains also two Croatian Glagolitic abecedariums, see one of them; according to Josip Hamm the whole cyrillic book of Radosav was transcribed from glagolitic original; Radosav wrote the Nikoljsko evandjelje, which was also transcribed from glagolitic original;
- the first and the second Glagolitic inscription from the vicinity of Banja Luka (Slatina) from 1471 (photos from [Poviest], see also [Fucic, Glagoljski natpisi -> Slatina]),
- Glagolitic muniments from Ostrozac, Ripac, Rmanja, Blagaj, Covac, Bihac, and Pec (mentioned by [Kresevljakovic]),
- Glagolitic inscription above the main entrance of Fehtija mosque in the town of Bihac in western Bosnia, designating the year 1527 in glagolitic characters (Cc, Fi, I, Zz). The mosque used to be the dominican church before the arrival of Turks. See [Fucic, Glagoljski natpisi, p. 96].
- Some glagolitic books are held in the Franciscan convent Gorica in Livno.  
- Glthe Manuscript of Krstyanin Radosav, 15th century (which contains three Glagolitic notes), held in the Library of De Propaganda Fide in Rome, etc.agolitic inscription with very cultivated letters, from Buzim near Bihac in western Bosnia (ie. Turkish Croatia), mentioning Prince Juraj Mikulicic, who built the fortress of Buzim against the Turks; mentions among others that “U nu vrime va vsei hrvatskoj zemlji boljega covika ne bise…” (ie. “At that time there was not a better man in the whole Croatian land…”, see the second line on the inscription below); it dates from the end of 15th century, and is held in the Museum of the City of Zagreb, see [Fucic, Glagoljski natpisi, p. 112].
- Bihac, 1543, cursive glagolitic document (Archives of Croatian Academy of Sciences and Arts in Zagreb, Acta Croatica), see [Lopasic, p. 301].
- Bihac, 1573, message written in the Glagolitic script about Turkish preparations to attack the town; with seven seals, see [Lopasic, p. 305].
- See [Jolic, Duvanjski popovi glagoljasi, pp 297-301], and [Damjanovic, Jezik hrvatskih glagoljasa]
There is no doubt that the oldest phase of the Bosnian and Herzegovinean literature was Glagolitic. Numerous Cyrillic manuscripts were translated from older Glagolitic books. This can be seen for instance in the Mostar Evangelistary from the 14th century, written by Mihajlo Grk, held in the Archive of the Serbian Academy in Belgrade. The last three glagolites in Bosnia died in 1834.
The last known glagolitic priest in Bosnia was Jakov Čotić (1727-1807), nicknamed Jako Čota, who lived in Kupres (Rastično). See Glas koncila, 6. June 2010. Here is an interesting monument from central Bosnia with inscription for which it is difficult to decide is it Croatian glagolitic, cyrillic, or something else:
It is interesting that in 1390, Jadwiga, the Polish Queen and her husband Wladyslaw Jagiello (Vladislaus Jagiello), founded a Glagolitic monastery under the invocation of The Saint Cross. It was established in Kleparz, the quarter of Krakow. Glagolitic liturgy existed there for about 100 years. Queen Jadwiga’s mother was the princess Elzbieta Bosniaczka, that is, Elizabeth of Bosnia.