The very beginnings of what was to become the Russian Orthodox Church began when Apostle Andrew, who it is said visited the Greek colonies via the Black Sea and Scythia during his travels. When he finally reached the spot that later became Kiev who prophesied that there would be a great Christian city built upon that site, and erected a cross on the spot that now houses the great St. Andrews Cathedral.
Around the same time when the Slavic lands came under the cultural influence of the Eastern Roman Empire, Saints Cyril and Methodius were busy translating the bible into the Old Church Slavonic language which opened the door for Christianity to begin flourishing among the peoples of the Eastern Europe and Balkans regions and well into Southern Russia.
The Christian community was already established in the Kiev nobility by the 10th century, and was under the influence of the Byzantine Greek priests, but on the whole paganism was still the dominant belief system. Around 945-957 AD, the Princess of Kiev, Olga, became the 1st ruler to officially convert to Christianity and her Grandson Vladimir made Rus the official Christian state and ordered that all his people be baptized by the priests from the Eastern Roman Empire.
While it would be many more centuries before Christianity would successfully spread across the European regions, and the Russian Orthodox Church would dominate the landscape, it was these beginnings that allowed the Christian religion to gain its foothold in the world.
During the Mongolian invasion, the city of Kiev began to lose its foothold as the cultural, economic and political center of the nation, and the Church moved its Metropolitan, the leader of the Church to Moscow.
The power the Church held was evident in that the Mongolians understood its potential influence and were not only tolerant of the Church but even granted it tax exemptions. This allowed the Church to consolidate its power and continue its work that would eventually become the Russian Orthodox Church began to take a deeper and more meaningful root.