Historians point to the rule of the Piast dynasty as crucial to the formation of the Polish state. However, some differentiate between members of the dynasty like Mieszko II Lambert, who ruled as king from 1025 to 1031 CE, and less well-documented figures like Siemomysł, who is said to have ruled in the 10th century but whose historical actuality is disputed. Siemomysł appears in the Gesta principum Polonorum, a chronicle of medieval Polish history written between 1112 and 1118. However, the chronicle’s documentation of Siemomysł relies on oral tradition, unlike its records of later rulers.