The honest elder was born in Pereyaslavl to Orthodox parents. Upon reaching adulthood, he became known to the great prince Ivan Vasilyevich, teaching him archery. Realizing the vanity of the world, he came to the monastery to the igumen Pafnutiy and was tonsured a monk with the name Kassian.
Kassian displayed humility and obedience, laboring in fasting and prayers. The igumen Iosif, seeing his zeal, intended to establish a communal life in the monastery. After the death of igumen Pafnutiy, Iosif became the igumen and began gathering like-minded individuals to realize his plan.
Iosif visited monasteries, seeking the best rules for the salvation of souls and found them in the monastery of Saint Cyril. At the site of the future abode, a sign occurred: lightning illuminated the ground. Iosif began to labor with the brethren, and Kassian joined them, taking upon himself a breastplate and laboring in prayers.
Kassian aspired to strict fasting, but igumen Iosif forbade him from excessive efforts. After long sufferings and prayers to the Most Holy Theotokos, Kassian was healed and promised not to wear shoes for the rest of his life. He endured cold and suffering, remaining in his monastic robe.
In old age, at the age of 90, his health weakened, and the brethren removed the heavy chains from him. After recovering, he again took upon himself light chains and continued to labor until his death.
