During the 10th century, the Lechitic Western Polans ("Polanie", lit. "people of the open fields") turned out to be of decisive historic importance. Initially based in the central Polish lowlands around Giecz, Poznań and Gniezno, the Polans went through a period of accelerated building of fortified settlements and territorial expansion beginning in the first half of the 10th century. Under duke Mieszko I of the Piast dynasty, the expanded Polan territory was converted to Christianity in 966, which is generally regarded the birth of the Polish state. The contemporary names of the realm, "Mieszko's state" or "Gniezno state", were dropped soon afterwards in favour of "Poland", a rendering of the Polans' tribal name. The Piast dynasty would continue to rule Poland until the late 14th century.