As the oldest son Siemowit obtained the central part of Masovia, with Rawa Mazowiecka (capital) Sochaczew, Zakroczym, Gostynin, Ciechanów and Wizna.
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As a potential successor Casimir III the Great on the throne of Poland, Siemowit II agreed to waive the rights of Chełmno and Eastern Pomerania.
Siemowit IV | Duchy of Masovia | Siemowit II of Masovia | Siemowit III | Janusz III of Masovia |
In 1326 the Grand Master formed an anti-Polish coalition at Brodnica, consisting of the Masovian dukes Siemowit II, Trojden I and Wenceslaus of Płock as well as of several Silesian Piasts and King John of Bohemia.