The arrival of Christianity was one of the earliest turning points in Russian civilisation. As the people of Kiev gathered to be baptised at the Dnieper River in the summer of 988, they were accepting a new order and a new identity. They were saying goodbye to an old pagan world.
Ruled by feuding princes from Kiev, Russia in 988 - known as Kievan Rus - was a loose federation of tribes. When the seventh prince - Vladimir - came to power he recognised the need for something to unify them. And he found it in the Christianity of eastern Orthodoxy.
Vladimir was mainly motivated by aesthetic reasons. His envoys watched a service in the Saint Sophia cathedral and came back saying: "We didn't know if we were in heaven or earth for we had never seen such beauty". Vladimir was converted and his people followed.
Christianity took root, in the landscape, lifestyle, art and culture of Rus. The tradition continued later in Russia, Belarus, and modern day Ukraine - where the main celebrations are taking place this year.
In today's Russia, this is a double anniversary. After seventy years of persecution at the hands of the Soviet regime - the thousandth anniversary in 1988 brought a second turning point. It was then that the church began to move out of the very limited space it inhabited within the walls of a few still open cathedrals.
So a millennium and two crucial decades on - Orthodox believers look to their church as an example of longevity and resilience.