The first ruling dynasty, the Piasts, emerged in the 10th century AD. Duke Mieszko I is considered the "de facto" creator of the Polish state and is widely recognized for his adoption of Western Christianity in 966 CE. Mieszko's dominion was formally reconstituted as a medieval kingdom in 1025 by his son Bolesław I the Brave, known for military expansion under his rule. The most successful and the last Piast monarch, Casimir III the Great, presided over a period of economic prosperity and territorial aggrandizement before his death in 1370 without male heirs. The period of the Jagiellonian dynasty in the 14th–16th centuries brought close ties with the Lithuania, a cultural Renaissance in Poland and continued territorial expansion as well as Polonization that culminated in the establishment of the Polish–Lithuanian Commonwealth in 1569, one of Europe's largest countries.