Mieszko I of Poland and half a century later, by Bishop Thietmar of Merseburg. By the time Mieszko I took over from his father, the Polans' tribal federation of Greater Poland had for some time been actively expanding. Continuing this process, perhaps in the first years of Mieszko's reign, if it had not been done already by his father, Mieszko I conquered Masovia. Likely also during that period or earlier, at least partially Gdańsk Pomerania was obtained. Mieszko's interests were then concentrated mainly on areas occupied by the eastern (near the Oder River) branches of the Polabian Slavs; some of them became soon subordinated
Mieszko the Younger point, Mieszko III decided to give the district of Kalisz to his youngest son and namesake, as his own Duchy. Mieszko the Younger died on 2 August 1193. He was buried in the crypt founded by his father in the Cathedral of St. Paul the Apostle in Kalisz. Tombstones of Mieszko the Younger and Mieszko III were found during archaeological excavations during 1958–1960. For unknown reasons, Mieszko never married or had children. On his death, Mieszko III give Kalisz to his eldest son Odon. Mieszko the Younger Mieszko the Younger (also known as of Kalisz) () (between 1160 and 1165