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 II the Fat Mieszko II the Fat Mieszko II the Fat () ( – 22 October 1246) was a Duke of Opole-Racibórz from 1230 until his death, and Duke of Kalisz-Wieluń during 1234–1239 (with his brother as co-ruler). He was the eldest son of Duke Casimir I of Opole by his wife Viola, probably a Bulgarian lady. At the time of his father's death in 1230, Mieszko II and his younger brother Władysław were still minors; for this, the regency of the Duchy was taken by their mother and Henry I the Bearded, Duke of Wrocław. Following her late husband's politics, the Dowager