Duchy of Masovia

The Duchy of Masovia was the Piast principality of the Polish northeast, existing from 1138 to 1526. It was born from a father's will: when Bolesław III Wrymouth died in 1138, his testament quartered Poland among his sons, and Masovia fell to the share that became a district duchy. Ruled by its own Piast line from Płock, Czersk and in time Warsaw, the duchy spent four centuries breaking apart and mending: Kuyavia, Dobrzyń, Czersk, Płock, Warsaw, Rawa and Belz all took turns as separate dukedoms before drifting back. The Masovian dukes played the familiar Piast game, marrying Lithuanians, quarrelling with the Teutonic Knights, and growing rich on Vistula grain while Warsaw slowly outgrew its elders. When the last dukes of the line died childless in 1526, King Sigismund the Old folded Masovia directly into the Polish Crown. Warsaw kept growing, and two generations later it became the capital of all Poland.