Cosmas of Prague
Boleslaus's reign is most notable for the foundation of the Diocese of Prague in 973, which earned him the epithet "The Pious" by the medieval chronicler Cosmas of Prague. Nevertheless, the Bohemian diocese was placed at that time within the jurisdiction of the Archbishop of Mainz, and Emperor Otto II enforced the appointment of the Saxon monk Thietmar ("Dětmar") as first bishop.