Casimir I, Duke of Cieszyn

Casimir I of Cieszyn (Polish: Kazimierz I cieszyński, Czech: Kazimír I. Těšínský, German: Kasimir I. von Teschen; 1280/90 – c. 29 September 1358), was Duke of Cieszyn from 1315, Duke of Siewierz from 1337 and Duke of Bytom from 1357.

He was the second son of Mieszko I, Duke of Cieszyn by his wife, probably called Grzymisława.

After death of his father in 1315, Casimir I gained the southwestern part of the duchy, centered around the town of Cieszyn. His marriage to Euphemia of Czersk founded a tradition of relationships of Cieszyn Piasts with Masovian Piasts.

Casimir I initially had good relations with Władysław I the Elbow-high, who became the King of Poland in 1320. But when during 1321–1324 Lithuanian forces supporting Elbow-high plundered Cieszyn, Casimir I broke with the Polish King. He then became a closer ally of John of Luxembourg, King of Bohemia and swore homage to him on 8 February 1327 in Opava; in exchange for his submission, Casimir I received the promise of inheritance of Oświęcim. Fifteen days later, on 23 February, he received Cieszyn as a hereditary possession, maintaining a large internal sovereignty.

Casimir I wanted to maintain the territorial unity of his Duchy, so he chose only one of his sons to be his successor — firstly the eldest, Władysław, and after his early death in 1355 the third, but the only one who remained outside the Church, Przemysław Noszak — and the others were destined for a Church career. In 1337 he acquired the districts of Siewierz and Czeladź from the Dukes of Bytom by 720 fines; also, he (temporarily) took the town of Namysłów from the Dukes of Brzeg, as a part of the dowry of his daughter Anna.

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