The early Ottoman Empire had no regulated succession, and according to Turkish tradition, every son could succeed his father. Of Mehmed's brothers, the eldest, Ertuğrul, had died in 1400, while the next in line, Mustafa, was a prisoner of Timur. Leaving aside the underage siblings, this left four princes—Mehmed, Süleyman, İsa, and Musa, to contend over control of the remaining Ottoman territories in the civil war known as the "Ottoman Interregnum". 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".