Vlachs in medieval Bosnia and Herzegovina were a Western Balkans population descending from a mixture of Romanized pre-Slavic Romance-speaking peoples and the South Slavs. From the 14th century the ethnic meaning of term "Vlach" was replaced with societal meaning and often meant the Slavic population with similar lifestyle. They practiced transhumance as herdsmen, shepherds, farmers, and in time developed peculiar socio-political organizational units known as katuns. With their caravans, Vlach carried out much of the traffic between inland and coastal cities such as Dubrovnik. They also had close contacts and militarily served various Bosnian noble families and kings.
History
In older scholarship, Marko Vego argued that Vlach autochthony because some Vlach settlements named after Vlach tribes, like of Vojnići and Hardomilje, are found near Roman forts and monuments, while Bogumil Hrabak supported Vego's assertion that the Vlachs preceded both Turks and Bosnian Slavs in Zachlumia, but by now it is certain that they emerged only as a medieval symbiosis of both autochthonous and Slavic peoples. Hrabak and Dominik Mandić argued that some Vlachs from Herzegovina migrated there from Thessaly, Epirus and Macedonia before the Ottoman invasion into Southern Europe, but although probably happened some waves of small migrations from there and Albania to Montenegro, Serbia and Bosnia and Herzegovina, for such theorization there's is lack of evidence and loose onomastic correlations cannot be used as generalized evidence of a certain linguistic and geographic origin of an individual.
Vlachs are first mentioned in Bosnian documents in c. 1234 by ban Matej Ninoslav. Sources from 1361, 1385, 1399, 1406, 1407, 1408 and 1417 among others mention them in relation to Bosnian bans and kings Vlachs in the Bosnian state of Tvrtko I were considered as military element. The relationship of Vlach katuns and feudal holdings can be traced from the 14th century. By 1382 they were under the jurisdiction of the Bosnian ruler, to later be assigned to large landowners. The Vlachs and lords relationships indicate that medieval Bosnia was not compact – some Vlach vassals (Gleđević) of the rulers were far from royal lands. Some Vlach vassals (Nenko Krajsalić, Radoslav Borojević) became vassals fairly late although Kosača ruled certain lands near Eastern banks of Neretva river for fifteen years. Some Vlach vassals (Maleš) were partly Pavlović and partly Kosača vassals although working on Kosača holdings.
In 1382, Vukoslav Piščić was named as knez of all Vlachs by King Tvrtko I of Bosnia. As the earliest noble landowners, in Herzegovina they were assigned to the Sanković noble family, with katun Tomić. In 1409, when Tvrtko I conquered parts of Rascia and Zeta they were located around 100 katuns. They were mentioned as "Vlachorum congregationes et cetus". In the area around Stolac and Zabljak were so many Vlachs that at the end of the 15th century the territory was as Donji Vlasi (Lower Vlachs). The Gornji Vlasi (Upper Vlachs) were only mentioned by Mavro Orbini.
The 1376 and 1454 documents by Republic of Ragusa about trade with Bosnian lands mention Vlachi et Bosgnani. In the 1418 document by Grgur Nikolić, Vlachs, Serbs and Ragusians are clearly distinguished. In the 14th century documents, they are treated as shepherds from mountains that separate Croatia and Bosnia. It is argued that some group of Vlachs in the 14th century migrated to Zagora and Cetina county in Croatia, followed by the sudden appearance of stećaks in the territory they lived. In 1436, on the Cetina are mentioned Vlachs, Croats and Serbs which were part of Count Ivan Frankopan’s estate. At a time of social unrest, the Vlachs often fled to the area of Ragusa or Kotor, served in the military of Ragusa during the Ottoman threat, and when most of Herzegovina was occupied by the Ottomans by 1472, once again fled to Ragusan territory. Some data of historic documents show that a part of Vlachs were Bogomils and they largely contributed to the spread of this sect. According to Sima Ćirković, ethnicity's which appear in the medieval texts from Bosnia include names such as "Bošnjanin", "Vlach", "Latinin" and "Serb".