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, Duke of Cieszyn The Obituary of the Church of St. Vincent in Wrocław showed the existence of a certain "Grzymisława, Duchess of Opole" ("Grimizlaua ducissa Opuliensis") who was buried there around 13 September 1286. Her parentage is also unknown, but her name suggests a Russian origin, probably member of the Rurikids. Her title suggests that she may have been the wife of Mieszko I or the first wife of Bolko I (Mieszko I's brother), or maybe a completely different person. Also, the exact date of their marriage was uncertain, but after a further reconstructions of their children's birth dates, was placed between 1275