Boleslaus was an elder son of Duke Boleslaus I the Cruel and brother of the three other children of his father who survived to adulthood: Strachkvas, Dobrawa and the abbess Mlada. His mother may have been Biagota, a mysterious figure known only from her coins. According to some historians, she was the wife of Boleslaus I.
Alliances
Boleslaus II took over the rule of the Duchy of Bohemia as kníže on his father's death in 972. Like his father, Boleslaus II initially quarrelled with the Ottonian kings of Germany. In 974 he and Duke Mieszko I of Poland supported the rebellious Duke Henry II of Bavaria in his civil war against the rule of Emperor Otto II. In 976, Henry was defeated and fled to Boleslaus' court at Prague Castle, whereafter Otto's forces campaigned the Bohemian lands. Finally in 978, Boleslaus solemnly pledged allegiance to the emperor at the Easter festivities in Quedlinburg. In turn, the relations with Poland deteriorated from about 980 onwards. When Emperor Otto II died in 983 and was succeeded by his minor son Otto III, the alliance was overturned, as Boleslaus again allied with the insurgent Bavarian Duke Henry, while Mieszko I took the side of the young king. Moreover, when Boleslaus occupied the SaxonMargravate of Meissen, he thwarted the plans of Mieszko's son Bolesław, who had married a daughter of Margrave Ricdag. In 987 Boleslaus had to retire from Meissen; from about 990, he sparked a long-lasting conflict with Poland around the lands of Silesia and Lesser Poland. In 992 he approached King Otto III and participated in an unsuccessful campaign against the Luticitribes in the wake of the 983 Great Slav Rising.
Unification of the Bohemian lands
Boleslaus's reign is most notable for the foundation of the Diocese of Prague in 973, earning 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 as first bishop. Meanwhile, the struggle with the rivalling Slavník dynasty flared up again from 981 onwards, when Prince Soběslav striving for independence began to forge alliances with the Polish and Saxon rulers. Upon Bishop Dětmar's death in 982, Soběslav's brother Adalbert was appointed his successor until he abandoned his primacy to lead a mission to the Old Prussians in 994. On 28 September995, Boleslaus' forces and the confederate Vršovci clan stormed Libice Castle in southern Bohemia and massacred the members of the Slavník dynasty that were found there. Boleslaus's brutal triumph ensured the unity of Bohemia under a single ruler.
Marriages and issue
Boleslaus's first wife Adiva may have been a daughter of the English kingEdward the Elder, though the evidence for this is weak. His second wife was Emma of Mělník. It is certain the Boleslaus's oldest son was born by Adiva, but the mother of the others cannot be established with certainty:
Soon after his father's death, Boleslaus III entered into conflict with his brothers and was deposed in 1002. The internal struggles of the Přemyslid dynasty shook the Bohemian duchy, until Duke Oldřich's efforts stabilised the country.
