Masovia

Following the death of Bolesław III in 1138 Poland was devided in dukedoms, according to his testament. Masovia was one of these duchies, and it was governed by a branch of the Piast dynasty till 1526. In 1351 the dukes of Mazovia became vasals of the Polish kings. And the Masovian bishopric of Plock was always part of the Polish archidiocese of Gniezno. Since the Polish-Lithuanian Union of 1385 it was localized between the joined Jagiellonian states. It is now located in east-central Poland and it's largest city Warsaw is also a Polish capital.