Sts Cosmas and Constantine were monastic followers of St Barlaam of Khutyn (November 6) and his successor, St Anthony of Dymsk (January 17). About the year 1220, they left the Khutyn monastery and settled upon a wilderness peninsula, situated 3 versts from the city of Staraya Rus, between the Rivers Polista and Smezhnya. In time they founded a monastery there in the name of St Nicholas, headed by St Constantine until his death (ca. 1240).
St Cosmas continued with the exploits of his mentor. He was buried in the same grave with St Constantine. Their bodies rest beneath the vestibule of the Nikolaev church, built in 1820 over the tomb of the saints.