History of Poland during the Piast dynasty of Lesser Poland, the country of the Vistulans, and of Silesia (both taken by Mieszko from the Czech state during the later part of the 10th century), Mieszko's state reached its mature form, including the main regions regarded as ethnically Polish. The Piast lands totaled about in area, with an approximate population of under one million. Initially a pagan, Mieszko I was the first ruler of the Polans tribal union known from contemporary written sources. A detailed account of aspects of Mieszko's early reign was given by Ibrâhîm ibn Ya`qûb, a Jewish traveler, according to whom Mieszko was one of
Mieszko III the Old of the rebels and divided Henry's Duchy in three parts: Wiślica Land was taken by Casimir, Bolesław took Sandomierz proper, and the rest was led to Mieszko. In 1172 another conflict arose among the Silesian Piasts, when Duke Bolesław the Tall chose to ignore the claims of his first-born son, Jaroslaw by designating his son of the second marriage Henry I the Bearded his sole heir. When Jarosław, forced to become a priest, had returned from his German exile, he claimed a share of the Silesian lands. Mieszko III supported his grandnephew in his demands, and the civil war was