citation for you from ms encarta article poland there is nothing like supposition about history of the recovered territories if you prefer you can check it in other encyclopaedia like britannica or some other neutral of course good lack with studies the piast dynasty mieszko converted the poles to christianity in order to compete better with the crusading and marauding germans during the reign of his son boleslaw i the christian church was firmly established in poland boleslaw also conducted successful wars against holy roman emperor henry ii and considerably expanded the polish domain he was crowned king by the pope in at his death poland extended beyond the karpaty mountains carpathian mountains and the odra and dniester rivers