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 to the Warta River). In all probability Mieszko decided to pay tribute in order to avoid an invasion similar to the one that Lusatia had suffered. This homage would take place in 965, or in 966 at the latest. Very likely the tribute applied only to the Lubusz land, which was in the German sphere of influence. This understanding of the tribute issue explains why already in 967 Mieszko I was described in the Saxon chronicles as the Emperor's friend (or ally, supporter, Latin: "amicus imperatoris"). Probably in 964 Mieszko began negotiations with the Bohemian ruler Boleslav I the Cruel.