Siemowit V of Masovia

Siemowit V of Rawa (pl: Siemowit V rawski; 1389 - 17 February 1442), was a Polish prince member of the House of Piast from the Masovian branch. He was a Duke of Rawa Mazowiecka, Płock, Sochaczew, Gostynin, Płońsk, Wizna and Belz during 1426-1434 jointly with his brothers, and after the division of the paternal inheritance between him and his brothers in 1434, sole ruler over Rawa Mazowiecka, Gostynin and Sochaczew.

He was the eldest son of Siemowit IV, Duke of Masovia and Alexandra of Lithuania, daughter of Algirdas.

He spent his early years at the court of King Władysław II Jagiełło in Kraków. In 1410 he took part alongside the Polish King in the Battle of Grunwald. In 1416 he assisted with the King at the Council of Constance and also took part of the Polish entourage during the meeting of the King with Sigismund of Luxembourg at Kežmarok.

After 1420 Siemowit IV, due to his progressive blindness, gradually gave participation in the government to his oldest sons, Siemowit V and Casimir II, who were formally named co-rulers. The first major challenge for Siemowit V was the trip to Brest-Litovsk, where on 14 November 1425 he and his brother solemnly vowed to the crown his fidelity and acceptance in the recent controversy who followed after the appointment of Stanisław z Pawłowic (former Chancellor of Siemowit IV) as Bishop of Płock.

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