Siemowit IV

Siemowit IV (Ziemowit IV), also known as Siemowit IV the Younger (pl: Siemowit IV Młodszy; ca. 1353/1356 – 21 January 1426), was a Polish prince member of the House of Piast from the Masovian branch, from 1373/74 Duke of Rawa, and after the division of the paternal inheritance between him and his brother in 1381, ruler over Rawa, Płock, Sochaczew, Gostynin, Płońsk and Wizna, since 1386 hereditary Polish vassal, since 1388 ruler over Belz, during 1382–1401 he lost Wizna and during 1384–1399 and 1407–1411 he lost Zawkrze, during 1384–1399 he lost Płońsk, taken by the Teutonic Order.

He was the second son of Siemowit III, Duke of Masovia and his first wife Euphemia, daughter of Nicholas II of Opava.

Already during his father's lifetime, Siemowit IV received his own district, Rawa Mazowiecka (ca. 1373/74), and as a result of the partition of Masovia between him and his older brother Janusz I after the death of their father on 16 June 1381, Siemowit IV finally obtain the totality of his domains: Rawa, Płock, Sochaczew, Gostynin, Płońsk and Wizna.

Siemowit IV chosen to be opposed to his older brother Janusz I in the relations with the Polish Kingdom - in particular, when he attempted to obtain the royal crown. One year after the acquisition of his own domains, King Louis of Poland and Hungary died (10 September 1382), and with this emerged the opportunity to place his candidacy to the crown, supported by the Greater Poland and Kujawy nobility (centered around the powerful Bartosz Wezenborg). However, the late King had made arrangements among the Lesser Poland nobility who guaranteed the support to his eldest daughter and heiress Mary and her husband Sigismund of Luxembourg. Without waiting for a favorable settlement, in January 1383, Siemowit IV marched to Greater Poland at the head of his troops, marked the beginning of the Greater Poland Civil War.

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