Siemowit III of Masovia

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Siemowit III of Masovia (his name also rendered Ziemowit; c. 1320 – 1381) was a prince of Masovia and a co-regent (with his brother Casimir I of Warsaw) of the lands of Warsaw, Czersk, Rawa, Gostynin and other parts of Masovia. A tributary to the king of Poland Casimir III, since 1370 he was a sovereign ruler of his domain. He granted his sons (Siemowit IV, Duke of Masovia and Janusz I of Warsaw) with separate domains centred around Warsaw and Rawa, leaving the core of his domain with Płock under his direct rule.