 In modern historiography, these princes are usually called by the title "Çelebi", but in contemporary sources, the title is reserved for Mehmed and Musa.The Byzantine sources translated the title as "Kyritzes" (Κυριτζής), which was in turn adopted into Turkish as "kirişçi", sometimes misinterpreted as "güreşçi", "the wrestler".After winning the Interregnum, Mehmed crowned himself sultan in the Thracian city of Edirne that lay in the European part of the empire (the area dividing the Anatolian and European sides of the empire, Constantinople and the surrounding region, was still held by the Byzantine Empire), becoming Mehmed I.