Title: Poslanieto na t︠s︡arigradskii︠a︡ patriarkh Fotii︠a︡ do bŭlgarskii︠a︡ kni︠a︡z Boris
Subjects: Sources, History, Schism, Eastern and Western Church, Bŭlgarska pravoslavna t︠s︡ŭrkva
People: Photius I Saint, Patriarch of Constantinople (approximately 820-approximately 891), Boris I Khan of Bulgaria (-907)