Boleslav II the Pious (died February 7, 999) was the son of Boleslav I the Cruel. Boleslav II became Duke (or Prince) of Bohemia in 972. Boleslav maintained good relations with the German Kingdom, and in 975 supported Otto II during his civil war against Henry of Bavaria. In 977 Boleslav again attacked Bavaria, but on this occasion was barred from annexing any lands by Otto II.
Boleslav's reign is mostly notable for the foundation of the bishopric of Prague in 973. It was placed within the jurisdiction of the Archbishop of Mainz. In 982 Vojtech (later known as Saint Adalbert of Prague) was appointed to this position until in 994 he abandoned his primacy to lead a mission to the Prussians. On April 23, 997 Adalbert was martyred in Prussia near Gdansk. His bones later became the holiest relic of Poland. War between Poland and Bohemia was continual in this period and by 990 Boleslav had occupied Silesia.
On September 28, 995 Boleslav stormed Libice in southern Bohemia and massacred the Slavnikovci. This clan had been the main rival of Premyslid power in Bohemia. Boleslav's brutal triumph ensured the unity of Bohemia under a single ruler.