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 in the entry for the year 985 it is noted that Mieszko came to help the Saxons in their fight against some Slavic forces, presumably the Polabians. One year later, the Polish ruler had a personal meeting with the Emperor, an event mentioned in the "Annals of Hersfeld": According to Thietmar and other contemporary chronicles the gift given by Mieszko to the Emperor was a camel. The meeting consolidated the Polish-German alliance, with Mieszko joining Otto's expedition against a Slavic land, which "together they wholly devastated (...) with fire and tremendous depopulation". It is not clear which Slavic territory was