 Complete the following phrase:  As the power of the Lithuanian warlord dukes expanded to the south and east, the cultivated East Slavic Ruthenians exerted influence on the Lithuanian ruling class. They brought with them the Church Slavonic liturgy of the Eastern Orthodox Christian religion, a written language Chancery Slavonic that was developed to serve the Lithuanian courts document-producing needs for a few centuries, and a system of laws. By these means, Ruthenians transformed Vilnius into a major center of Kievan Rus civilization. By the time of Jogailas acceptance of Catholicism at the 