Foundation of Poland was laid in the mid-10th century when Duke Mieszko I, a ruler of Western Slavic tribes married Doubravka,princess of Bohemia.Mieszko I embraced Christianity in 966 and so did his people.The Polish flourished under various rulers till the 13th century till they were invaded by the Mongols.Although the Polish lost in the Battle of Legnica in 1241,the Mongols decided to withdraw.