Sergius of Radonezh and the Trinity monastery

Bartholomew's family came from Rostov; according to his Life by Epiphanius the Wise, it was ruined by a Tatar punitive raid and by the Muscovite takeover of Rostov under Ivan Kalita and moved to Radonezh, in the Moscow lands. After his parents' death he and his elder brother Stefan withdrew into the forest on Makovets hill, about ten versts from the Khotkovo monastery, and built a cell and a wooden church of the Trinity — then a rare dedication in Rus’. The Life gives no years: the traditional date of 1337 goes with a birth in 1314, while B. M. Kloss, who dates Sergius's birth to 1322, places the foundation in 1342. Stefan soon left for Moscow; Bartholomew was tonsured as Sergius and lived alone for some time before other monks settled around him.

In 1354, by the traditional dating, Sergius was ordained priest and became hegumen. Between the mid-1360s and the mid-1370s, in connection with a letter from Patriarch Philotheos of Constantinople, he replaced the old rule, under which each monk lived on his own, with a common life — shared property, meals and work — despite opposition within the brotherhood. His disciples founded new monasteries, from the Andronikov and Simonov in Moscow to houses in the northern forests, and spread the common rule across north-eastern Rus’. Metropolitan Alexius wanted Sergius as his successor, but he refused; he acted as a peacemaker among the princes and in the mid-1380s helped to bring about a lasting peace between Oleg of Ryazan and Dmitry Donskoy.

According to the Life, Dmitry Donskoy visited Sergius before marching against Mamai and received his blessing; the later Tale of the Rout of Mamai adds that Sergius sent two monks, Alexander Peresvet and Andrei Oslyabya, with the army. The historian V. A. Kuchkin has argued that the Life's story originally referred to the campaign of 1378 on the Vozha and was attached to the Battle of Kulikovo only later. Sergius died on 25 September 1392 and was buried in his monastery; his relics were uncovered in 1422, and by the middle of the 15th century he was venerated as a saint. The monastery became the greatest in Russia — today's Trinity Lavra of St Sergius in Sergiev Posad.