Mieszko I of Poland mentions a gift or dedication of Mieszko's land to the Pope (the act took place almost a hundred years earlier). It is roughly his borders that Poland was returned to in 1945. There is no certain information on Mieszko I's life before he took control over his lands. Only the "Lesser Poland Chronicle" gives the date of his birth as somewhere between the years 920–931 (depending on the version of the manuscript), however, modern researchers don't recognize the Chronicle as a reliable source. Several historians on the basis of their investigations postulated the date of Mieszko I's birth to have
Bolesław the Forgotten calendar was in use so New Year's Day had not been changed to the first day of January. The text describes him as follows: However, there is no mention of any coronation of a Polish ruler in this period, which would have to be recorded in the German sources (as was the case with the coronations of Bolesław I and Mieszko II), probably because there was no royal insignia in the country, which had been returned to the Emperor by the well-known Bezprym earlier in the year 1031. This brief description of Bolesław in the "Wielkopolska Chronicle" is very similar