Vladimir I Adopts Orthodox Christianity
Also called: Baptism of Rus’, Christianization of Kievan Rus’
In 988 Vladimir I of Kievan Rus’ converted to Orthodox Christianity on marrying the Byzantine emperor’s sister, bringing Rus’ into the Byzantine cultural world.

Viktor Vasnetsov · Public domain · Source
The chronicle relates that Grand Prince Vladimir I of Kyiv examined Islam, Judaism, Latin Christianity and Greek Orthodoxy before choosing the Orthodox faith of Byzantium. In return for sending troops to the Byzantine emperor Basil II, beset by rebellion, he married the emperor’s sister Anna and was baptised around 988. He had the people of Kyiv baptised in the Dnipro.
Rus’ thus took in Byzantine religion, script (Cyrillic), architecture and art and became a centre of the Orthodox world. This choice later underpinned Russia’s claim to be the “Third Rome”. At the same time King Seongjong of Goryeo was building a Confucian state, adopting Choe Seung-ro’s 28-article policy proposal.