Sergius, born Bartholomew around 1314 to a noble family of Rostov that had been reduced to poverty and relocated to Radonezh, near Moscow, took monastic vows in his early twenties after the death of his parents, choosing along with his brother Stefan to settle as a hermit in the dense forest at a place called Makovets. Stefan found the isolation unbearable and left for a monastery in Moscow, but Sergius remained alone for several years, and hagiographic tradition, recorded in the Life written by his disciple Epiphanius the Wise, describes wild animals, including a bear he reportedly fed from his own scant food, coming to his hermitage without harming him, a set of images later Russian iconography returned to repeatedly.
Other monks gradually gathered around him, drawn by his reputation for holiness, and the community that formed elected him abbot only after his consistent refusal to accept the position of authority himself. Sergius insisted on manual labor and communal poverty for the brotherhood at a time when Russian monasteries commonly supported themselves on individual cells and private means, a shift toward strict communal life, known as cenobitic monasticism, that spread from his monastery to found or reform dozens of others across northern Russia within a few generations.