15th–16th centuries

"Moscow, the Third Rome", and the establishment of the Moscow Patriarchate

The Union of Florence was accepted by a Greek metropolitan, but the Russians rejected it. They concluded that the Greek church had fallen while Russia remained the guardian of true Orthodoxy. The fall of Constantinople in 1453 reinforced this sense.

In the early 16th century the Pskov monk Philotheus formulated the idea: "two Romes have fallen, a third stands, and a fourth there shall not be". Moscow inherits from Rome and Constantinople as the last bastion of Orthodoxy. The "Third Rome" becomes a kind of theocracy centered on the emperor rather than the church. This tended toward caesaropapism.

An heir of this mystical tradition in Rus was Nil Sorsky. He often invoked Symeon the New Theologian and wrote of "the light which the world has not seen". Sergius of Radonezh dedicated a church to the Holy Trinity and founded the Trinity Lavra near Moscow. He became an example of hesychast mysticism on Russian soil.

The Moscow patriarchate was then established – in 1589, with the approval of the Eastern patriarchs (one book gives 1596).