The first historically documented Polish state, centered on Gniezno and ruled by the Piast dynasty. Duke Mieszko I (r. c.960-992) unified the Polans, defeated rival tribes, and adopted Christianity in 966, laying the institutional groundwork for the Kingdom of Poland.
Formally elevated into the Kingdom of Poland in 1025, when Mieszko I's son Bolesław I Chrobry was crowned the first King of Poland shortly before his death.
Polity-specific biography of the duchy's founding ruler, Duke Mieszko I; verified on Open Library. (Polish-language.)
Accessible English-language survey opening with the Piast-era duchy; secondary fallback for readers without Polish.