Russkaya Pravda
While Christianity had made headway into the territory of Ukraine before the first ecumenical council, the Council of Nicaea (325) (particularly along the Black Sea coast) and, in western Ukraine during the time of empire of Great Moravia, the formal governmental acceptance of Christianity in Rus' occurred in 988. The major promoter of the Christianization of Kievan Rus' was the Grand-Duke, Vladimir the Great ("Volodymyr"). His Christian interest was midwifed by his grandmother, Princess Olga. Later, an enduring part of the East-Slavic legal tradition was set down by the Kievan ruler, Yaroslav I, who promulgated the Russkaya Pravda (Truth of Rus') which endured through the Lithuanian period of Rus'.