In 1336 Bartholomew went to the solitude of Radonezh with his brother Stefan. At the age of 23, now known as Sergiy of Radonezh, he founded the Trinity Monastery (Sagorsk). Sergius also introduced many reforms of monastic life. The 14th century was predestined for this, as the connection between ecclesiastical and secular power in the rising Moscow was solidified at this time. For example, Alexander Nevsky’s grandson, Ivan I, also known as the Kalita, had the Koimesis Cathedral, Moscow’s first stone church, built in a year-long construction process, both at the instigation of Metropolitan Petr and the relocation of the metropolitan seat to Moscow in 1326. Ivan Kalita, who had held the dignity of Grand Duke since 1328, built the Kremlin out of wooden structures as early as 1329. Two major fires destroyed the facility again, but construction began again in 1339. Ivan I. Kalita, Prince of Moscow, died in 1340.
Sergius von Radonezh was involved in the founding of 40 monasteries and was highly venerated during his lifetime. Sergius once prayed in front of the icon of the Blessed Mother. After saying the prayer, a voice rang out: “The all-pure comes”. Sergius got up and stepped out of his cell. Then a great light poured out in which the Blessed Mother stood, next to her the two apostles Peter and John. Maria said, “Do not be afraid” and the light disappeared.