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 Archbishopric (which was also accused for "heresy"!), and to attach it to the Hungarian Archbishopric 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.