Wikipedia
Blac People
The Blacs were a people mentioned by several medieval authors. They did not leave any written material and their ethnicity is not clear from the contemporary chronicles. They were referred to as Blachorum, Blacorum, Blachos, Blachi. The term Blakumen or Blökumen might refer also to them. The majority of historians identify them with Vlachs but there are authors who suggest a Turkic origin. According to historical sources, found below, they lived somewhere around the Ural Mountains and the Volga River and then traveled west to the lower Danube area during the Migration Period.
Historical References
The writings of William of Rubruck from the mid 13th century present some of the Blacs as still living beside the Bashkirs (Pascatir) east of Great Bulgaria and the Volga River. He writes that the Tatars call them Illacs because the Tatars can not pronounce the letter B. Some of the Blacs migrated west with the Huns, Bulgarians and Vandals earlier and settled somewhere in the lower Danube area: from them come those who are in the land of Assan, those provinces from Constantinopole (westward) and which were called Bulgaria, Blackia and Sclavonia were provinces of the Greeks p130. He writes that they were Christians (at least one of the branches).
Anonymus in his work Gesta Hungarorum written in Latin around 1200 mentions the Blacs several times as living in Pannonia and Transylvania.
Several documents issued by Andrew II of Hungary between 1222 and 1224 mention some property names in southern Transylvania which bear their name ( Golden Bull of 1222, Diploma Andreanum: ' Terra Blacorum' (Land of the Blacs); Silvam Blacorum et Bissenorum (The Forest of the Blacs and Pechenegs)).
Simon of Keza wrote at the end of the 13th century the Gesta Hunnorum et Hungarorum. In it he mentions both the Blacs (Blackis) and the Vlachs (Vlahis), as such, differentiating them. He writes that the Szekelys (Zaculi) live together with the Blacs (Blackis) and use the Blacs' letters. The Szekelys historically used runes of Turkic origin. The Vlachs did not have a runic script.
Geoffrey of Villehardouin in his work De la Conquête de Constantinople (On the Conquest of Constantinople) written after 1207 about the 4th Crusade names Kaloyan of Bulgaria King of the Blacs. Contemporary papal sources name him ruler of Bulgars and Blacs.
Roger Bacon in his work Opus Majus (1265-1267) writes that the Blacs lived close to the Bashkirs, west of the Ural Mountains and now live on the land of Asen, north of the New Bulgars and between New Hungary.
Abulghazi, a Turkistani writer of the 17th century, calls the Volga Bulgarians olaks or ulaks in his Mongolian stories. Similarly, the Osman Turks called iflak their Vlach and Bulgarian rayas (taxpaying serfs), after they occupied the eastern Roman Empire.
The chapters III. and VIII. of Nestor's chronicle also mention Blacs . (They are coming out of Scythia conquering Bulgarians and Danube Slavs.)
The Persian historian Fazel-ullah Raŝid ( Rashid-al-Din Hamadani) also writes about the kara-ulagh people, who were dispelled by the Tatars in 1240, near the river Olt, when they invaded the country Bazaram.
In 1626, the Hungarian chronicler Gergely Pethő (c. 1570-1629) also writes about a 1198 military campaigng of king Emeric against the Bulgarians and Vlachs (probably Blacs).