Casimir I, Duke of Cieszyn

Casimir I (1280/1290–1358), second son of Mieszko I, became Duke of Cieszyn in 1315. At first close to King Władysław I of Poland, he switched sides after Lithuanian raids and swore homage to John of Bohemia at Opava in 1327, holding Cieszyn as a hereditary fief.

He secured half of Bytom in 1357, ringed Cieszyn with walls and promoted town life. He married Euphemia of Masovia, who bore him nine children, and died in 1358.