Early Life and Formation
Cyril was born Cosmas in Moscow in 1337 into a family close to the boyar house of Velyaminov. His parents died during his childhood, and he was raised by his kinsman Timothy Vasilevich Velyaminov at the court of Prince Dmitry Ivanovich Donskoy.
Around 1380 he was admitted to the Simonov Monastery in Moscow, where he took monastic vows under Theodore of Rostov and received the name Cyril. He served the community in a succession of manual labors — work in the bakery, water-carrying, wood-chopping, and kitchen duties — over a period of some nine years. Saint Sergius of Radonezh frequently visited him for spiritual conversation.
Leadership and Withdrawal
When Theodore of Rostov became Archbishop of Rostov in 1388, the Simonov community chose Cyril as their abbot. By some accounts he had briefly served as archimandrite in 1387. He found the office demanding too much involvement in public affairs, and as his reputation drew increasing numbers seeking spiritual guidance, he resigned in order to pursue a more contemplative life.
Following the counsel of Sergius of Radonezh, Cyril departed Simonov together with his companion Saint Therapon (Therapont) and traveled to White Lake (Lake Beloye) in northern Russia. The anchor account relates that he withdrew to the shores of White Lake at the bidding of the Mother of God.
Foundation of the Kirillo-Belozersky Monastery
Settling in the remote region near Lake Siverskoye, Cyril first dug a cave, then built a wooden chapel dedicated to the Dormition (Assumption) of the Mother of God and a loghouse for other monks. From these beginnings the Kirillo-Belozersky Monastery was established in 1397, with Cyril as its first hegumen.
Cyril governed under a strict cenobitic rule that emphasized silence and communal discipline. His companion Therapon, finding the discipline too rigorous, departed within a year to establish the nearby Ferapontov Monastery. Under Cyril's leadership the monastery acquired large areas of land and expanded into the largest monastery of northern Russia, a beacon of the region sometimes called the northern Thebaid.
The monastery continued to grow long after Cyril's death. Its principal Dormition cathedral was erected by Rostov masters in 1497, and by the 16th century the foundation had become the second richest landowner in Russia after the Trinity Monastery near Moscow. It withstood a Polish siege in 1612 and at times served as a place of exile for prominent figures.
Repose and Veneration
Cyril reposed at the monastery on June 9, 1427, in the ninetieth year of his life. His veneration began within decades of his death, by some accounts around 1448. A biography was commissioned by Metropolitan Theodosius and written by Pachomius the Logothete in 1462. He was formally canonized by the Makaryev Sobors of the Russian Orthodox Church in 1547.
Three surviving letters attributed to Cyril demonstrate his spiritual counsel to Russian princes, and sixteen works were attributed to him among the holdings of the monastery library, which contained over two thousand books by 1635.
