He is married to Sophie OF LITHUANIA.in the year 1279.
Boleslaw II of Masovia or Boleslaw II of Plock (c.1251- April 20, 1313). He was the younger brother Konrad II of Masovia and son of Siemowit I of Masovia. His mother was Pereyaslava, daughter of Daniel of Galicia.
Boleslaus became Duke of Masovia in 1262. In 1275, he shared Masovia with his brother and he became Duke of Plock. From 1294, Boleslaus reigned over all of Masovia. In 1288 he became Duke of Sandomierz. In 1310 he offered some of Masovia to his son (the Duchy of Warsaw and the Duchy of Czersk).
Duke of Plock
In 1262 Boleslaus' father, Siemowit was killed by the Lithuanians who also captured his brother. The regency of the duchy of Masovia was then ensured by Boleslaw the Pious and Boleslaus' mother Pereyaslava.
In 1275 when he reached the age of majority, Masovia was shared between him and his brother. He received the Duchy of Plock. Boleslaw did not like how much of the Duchy he was receiving and a prolonged conflict between the two brothers broke out. In 1279, there was an alliance with the Lithuanians and Boleslaus married Sophia, the daughter of Grand Duke Treniota of Lithuania. Boleslaus was also an ally of his cousin Wladyslaw I the Elbow-high, who was then Duke of Kuyavia.
Fighting for Krakow and Sandomierz
In September 30, 1288, Leszek II the Black died without leaving an heir. Part of the nobility of Lesser Poland supported the accession of Boleslaus. He faced Henry IV the Probus, the Duke of Wroclaw, who aimed to succeed in Krakow as well as Boleslaus did. In 1288, Boleslaus seized Sandomierz and Krakow. On February 26, 1289 he defeated Henry IV the Probus.
Despite the victory, the inhabitants of Cracow offered power to Henry IV rather than Boleslaus. Powerful Lesser Poland rallied to Henry IV, ending the hopes of Boleslaw ascending the throne in Cracow. This left the Duchy of Sandomierz to his brother Conrad II of Masovia. This dissatisfied the nobles of Lesser Poland, accustomed to see the Duke of Krakow reign over Sandomierz. Finally, Boleslaw left Lesser Poland to Wladyslaw I the Elbow-high and retired to his duchy. The only positive aspect of this struggle for the throne of Krakow was the reconciliation with his brother Conrad.
Alliance with Bohemia
Boleslaus' wife Sophia died so he remarried in early 1291 to Kunigunde, the sister of Wenceslaus II of Bohemia. The same year, Wenceslaus seized Krakow. Boleslaus saw his position strengthen. The following year, his stepfather came to his aid in his war against Wladyslaw I the Elbow-high.
Duke of Mazovia and war with Bohemia
The alliance between Masovia and Bohemia did not last very long. On October 11, 1294 Conrad II died, Boleslaus became ruler of all Masovia. Feeling stronger, he broke his alliance with Bohemia and turned to Wladyslaw I.
In 1295 Przemysl II became King of Poland. The following year, after the assassination of Przemysl II, Boleslaus and Wladyslaw went into a brief was against Henry III of Glogów for the succession in Poland.
In 1300, the deterioration of relations between Bohemia and Masovia pushed Wenceslas II to attack Masovia. Boleslaus resists and does not change his political line. He did not recognize Wenceslas as King of Poland so he returned Kunigunde to Prague in 1302, despite fathering three children by her.
In the early 1300s Boleslaus founded the stronghold of Warsaw. After 1305 the political activities of Boleslaus were reduced. In 1310 he transferred part of Mazovia to his eldest two sons. Siemowit receiveed the Warsaw area and Trojden received Czersk. In 1311, Borzyslaw becomes his Chancellor.
Boleslaus II of Mazovia died on April 20, 1313.
In 1279 he married firstly to Sophia, the daughter of Grand Duke Treniota of Lithuania, they had the following children:
Siemowit II of Masovia, Duke of Masovia (1310-1345)
Trojden I of Masovia, Duke of Masovia, Czersk and Warsaw (1310-1341)
Anna married Wladyslaw of Legnica, divorced
In 1291 he married Kunigunde, daughter of Ottokar II of Bohemia, they had the following children:
Wenceslaus of Plock (ca. 1293 - 1336), became Duke of Plock
Euphrosyne (b. ca. 1292 - d. 26 December 1328/29), married Wladyslaw of Oswiecim and had issue
Bertha (before 1299 - after 1311), nun at Monastery of St. George