The analysis of the oldest known Polish annals, namely the Ancient Annals, the Annals of the Cracow chapter and the Annals of Kamieniec enables us to reconstruct the formation of the memory of the first Piast rulers in the oldest Polish annals as well as the vision of the times of the first rulers of this dynasty contained in the lost archetype of Polish annalistics, that is to say the so-called Annales Regni Poloniae deperditi (ARPd). The study of the preserved annalistic material suggests that about half of the notes concerning Mieszko I and Boleslas the Brave in the Polish annalistic tradition were most probably already present in the ARPd. The attempt of reconstruction of the entries concerning Boleslas the Brave in the ARPd also shows that they concern mainly the last years of his reign, which suggests that the redaction of the ARPd started at the latest during the second decade of the XIth century.