became baptized, taking the "Christian name" Helen. Her baptism in 955 (or 957) in either Kyiv or Constantinople (accounts differ) was a turning point in religious life of Rus' but it was left to her grandson, Vladimir the Great, to make Kyivan Rus a Christian state. Both Vladimir and Olga are venerated as the Equal-to-apostles saints by the Eastern Orthodox Church. Princess Olga of Kyiv shortly after her baptism appealed to the Holy Roman emperor Otto the Great to send missionaries into Kyivan Rus. Saint Adalbert, a Latin missionary bishop from Germany, was sent, but his missions and the priests who missionized along with him, were stopped. Most of the group of Latin missionaries were slain by pagan forces sent by Olga's son, Prince Svyatoslav, who had taken the Crown from his mother. Christianity became dominant in the territory with the mass Baptism of Kyiv in the Dnieper River in 988 ordered by Vladimir. That year is considered as the year of establishment of the Kyiv Metropolis and part of the Ecumenical Patriarchate of Constantinople. The exact date of establishment is not clearly known as the Kyiv eparchy (metropolis) is mentioned as early as 891. The first cathedral temple, Church of the Tithes (Assumption of Virgin Mary), was built in 996. Following the Great Schism in 1054, the Kyivan Rus that incorporated some of the modern Ukraine ended up on the Eastern Orthodox Byzantine side of the divided Christian world. Early on, the Orthodox Christian metropolitans had their seat in Pereyaslav, and later in Kyiv. The people of Kyiv lost their Metropolitan to Vladimir-Suzdal in 1299 (who retained the title), but gained a new Metropolitan in Halych in 1303. The religious affairs were also ruled in part by a Metropolitan in Navahrudak, (present-day Belarus). After the breakup of the Kyivan Rus In the 15th century, the primacy over the Ruthenian Orthodox Church was moved to Vilnius, under the title "Metropolis of Kiev and all Rus'". One clause of the Union of Krevo stipulated that Jagiello would disseminate Catholicism among Orthodox subjects of the Grand Duchy of Lithuania, of which Ukraine was a part. The opposition from the Ostrogskis and other Orthodox magnates led to this policy being suspended in the early 16th century. Following the Union of Lublin, the Polonization of the Ukrainian church was accelerated. Unlike the Catholic Church, the Orthodox church in Ukraine was liable to various taxes