The name Ioannina appears for the first time in 879, in the acts of the Fourth Council of Constantinople, which refer to one Zacharias, Bishop of Ioannine, a suffragan of Naupaktos. After the Byzantine conquest of Bulgaria, in 1020 Emperor Basil II () subordinated the local bishopric to the Archbishopric of Ohrid. In the treaty of partition of the Byzantine lands after the Fourth Crusade, Ioannina was promised to the Venetians, but in the event, it became part of the new principality of Epirus, founded by Michael I Komnenos Doukas.