He became the 'Duke' of the Polan tribe in the 9th century after his peasant father, son of Chościsko, refused to take the place of legendary Duke Popiel. Siemowit was elected as new duke by the wiec. According to a popular legend, Popiel was then eaten by mice in his tower on the Gopło lake. [2]
The only mention of Siemowit, along with his son Lestko and grandson Siemomysł, comes in the mediæval chronicle of Gallus Anonymus. [3]
Mieszko I of the Piast dynasty is considered the first ruler of Poland to be baptized, though evidence of Arian Christians predating his reign was discovered in south Poland.