Kirillo-Belozersky Monastery, loosely translated in English as the Assumption monastery of St. Cyril, is founded in 1397; it will one day be the largest monastery of Northern Russia.

Its founder, Saint Kirill of Beloozero, following the advice of his teacher, Saint Sergius of Radonezh, had first dug a cave here, then builds a wooden Assumption chapel and a loghouse for other monks.

Being a member of the influential Velyaminov clan of boyars, Kirill relinquishes the office of father superior of the greatest cloister in medieval Moscow—the Simonov monastery.

His ties with the ruling elite are still close, however, as his letters to sons of Dmitri Donskoi clearly demonstrate.

It seems that the Muscovite rulers regard Kirill's monastery as an important strategic point, both for Northern trade and in their struggle with the Novgorod Republic.