Bolesław IV the Curly (; 1122 – 5 January 1173), a member of the Piast dynasty, was Duke of Masovia from 1138 and High Duke of Poland from 1146 until his death in 1173.
Early life
Bolesław was the third son of Duke Bolesław III Wrymouth of Poland by his second wife Salomea of Berg. The death of his older brothers, Leszek and Casimir, before 1131 and in October 1131, respectively, left him as the eldest son of their parents. Bolesław was 13 years old at the time of his father's death (1138) and of the legal age to take on the government of the lands he inherited according to his father's testament, the newly created Duchy of Masovia (composed of Masovia and eastern Kuyavia).
In the first years of his government, young Bolesław remained under the strong influence of his mother and Voivode Wszebor, who feared the ambition of his elder half-brother High Duke Władysław II. Władysław II tried to restore the unity of the country and deposed the junior dukes.
Fraternal struggle
Trouble began openly in 1141, when Dowager Duchess Salomea — without the consent of High Duke Władysław II — organized a meeting with her sons at her residence in Łęczyca. Here was decided the betrothal of her youngest daughter, Agnes, to Mstislav II of Kiev, in order to gain allies in a possible conflict. She also set up the division of the Łęczyca lands, her dower, between her sons upon her death. The junior dukes in this first struggle were definitely defeated, because Grand Prince Vsevolod II of Kiev decided to make an alliance with Władysław II, reinforced by the marriage of Vsevolod's daughter Zvenislava with the high duke's eldest son, Bolesław the Tall. An additional humiliation for Bolesław IV and his brothers was that they were sent by the high duke on an expedition to the Kievan Rus' as ambassadors during 1142–1143.
The "peace" lasted only two years until 1144 when, after Salomea's death and according to Bolesław III's Testament, the Łęczyca province reverted to the Seniorate Province of High Duke Władysław II. The idea to reserve the lands for his younger brothers Henry and Casimir II was not popular with Wladyslaw, who thought that the land was only temporarily separated from his Dzielnica senioralna and now in its entirety should be returned. The outbreak of civil war was therefore only a matter of time.
The war erupted with full force in 1145, and it seemed that the junior dukes were defeated and the high duke finally achieved the unification of the country. At first the combined forces of Bolesław IV and his brothers prevented the disaster and demanded a hasty reorganization of the forces of Władysław at the Battle on the Pilicą River. The major significance of this battle was to the former voivode Wszebor, whose military experience far exceeded the ability of Władysław's commanders. Soon, however, the situation was totally reversed as a result of the Kievan troops who entered in the country as Władysław's allies. Bolesław then had to agree to step down and renounce any pretension over the lands belonging to his mother.
The concessions of the junior dukes ultimately didn't resolve the problem. Moreover, Władysław's confidence in his forces had him embark on a final solution, the removal of his stepbrothers from their lands. Suddenly, the junior dukes could rely on the support of the high duke's all-powerful voivode Piotr Włostowic, for whom Władysław's plans were too radical and threatened to weaken his position. While Władysław opted for a quick response against him (the voivode was blinded and muted), forcing Włostowic to go to Kiev, the high duke's final decision on his confrontation with the voivode considerably weakened his position. What's more, Włostowic convinced the Kievans to break his alliance with Władysław.
Expulsion of Władysław II
At the beginning of 1146 the rebellions against Władysław's government rose mighty, sparked by the fate of Piotr Włostowic. Nevertheless, the final victory of Władysław seemed likely, especially after the conquest of Masovia (forcing Bolesław to escape) and the siege of Poznań in Greater Poland in the spring of 1146. However, thanks to the rebellion in Władysław's own lands, and the excommunication imposed to him by the Archbishop of Gniezno, the high duke suffered an unexpected defeat. Władysław and his family had to flee across the border with the Holy Roman Empire, at first to Bohemia and later to Germany, accommodated by King Conrad III.