Mieszko I of Poland elders, and limited their authority. Clergy who arrived in the country contributed to the development of education and culture, and of the state administration and diplomacy, as well. At the end of Mieszko's reign (ca. 990), Poland began to pay tribute to the pope (Peter's Pence). However, the conversion of the Polish population to Catholicism was a long-term process, and was not completed during the reign of Mieszko I. The duke probably had to deal with rebellions led by the old pagan priest caste. In some villages, the old Slavic beliefs and customs were continued until the 16th century. After
Mieszko I of Poland poses some problems of interpretation of the information regarding the attack of Margrave Gero on the Slavic tribes, as a result of which he purportedly "subordinated to the authority of the Emperor Lusatia and the Selpuli" (meaning the Słupian tribes) "and also Mieszko with his subjects". According to the majority of modern historians, Thietmar made an error summarizing the chronicle of Widukind, placing the Gero raid there instead of the fighting that Mieszko conducted at that time against Wichmann the Younger. Other sources make no mention of such conquest and of putting the Polans state on the same footing with