Duchy of Mazovia
| Duchy of Masovia | ||||||||||
| Księstwo Mazowieckie | ||||||||||
| Province of Poland Fiefdom of the Polish Crown (from 1351) |
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 Masovian lands (ziemie)
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| Capital |
Płock Czersk (from 1262) Warsaw (from 1413) |
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| Religion | Roman Catholic | |||||||||
| Government | Duchy | |||||||||
| Dukes | ||||||||||
| • | 1138–1173 | Bolesław the Curly | ||||||||
| • | 1194–1247 | Konrad I | ||||||||
| • | 1248–1262 | Siemowit I | ||||||||
| • | 1503–1526 | Janusz III (last) | ||||||||
| Historical era | Middle Ages | |||||||||
| • | Established | 1138 | ||||||||
| • | Split off Kuyavia | 1233 | ||||||||
| • | Partitioned | 1313 | ||||||||
| • | Vassalized by the Polish Crown |
1351 | ||||||||
| • | Second partition | 1381 | ||||||||
| • | Incorporated by Poland |
1526 | ||||||||
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The Duchy of Masovia (Polish: Księstwo Mazowieckie; Mazovian: Xjãstfo Mazovii) with its capital at Płock was a medieval duchy formed when the Polish Kingdom of the Piasts fragmented in 1138. It was located in the historic Masovian region of northeastern Poland. Masovia was reincorporated into the Jagiellon Polish kingdom in 1526.
The lands of the Masovians east of the Vistula river had been conquered by Duke Mieszko I of Poland (960–992) and formed a constituent part of the Civitas Schinesghe under the Piast dynasty. The Diocese of Płock had been established in 1075.
Following the death of Duke Bolesław III Wrymouth in 1138, as specified by his testament, the Masovian province was governed by his second son Bolesław IV the Curly, who, after he had expelled his elder half-brother Władysław II, in 1146 became Grand Prince (High Duke) of Poland. His Masovian realm also comprised the adjacent lands of Kuyavia in the west.
Among the Piast Dukes of Masovia, Bolesław's IV nephew Konrad I was High Duke from 1229 to 1232 and again from 1241 to 1243; he was the ruler who called the Teutonic Knights for help against the pagan Old Prussians threatening the northern borders of his territory. In turn he ceded the Prussian Kulmerland to the Knights in 1230, which according to the 1235 Golden Bull of Rimini (dated 1226) issued by Emperor Frederick II of Hohenstaufen became the nucleus of the Order State. In 1233 Konrad gave Kuyavia to his second son Casimir I, while Masovia passed to the first-born Boleslaus I upon his death in 1247, succeeded by the youngest brother Siemowit I the next year.
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Wikipedia