Around 1371 Euthymius returned to Bulgaria and founded the Holy Trinity Patriarchal Monastery near Tarnovo, where he grounded the Tarnovo Literary School. He established orthographic rules and corrected inaccurately translated religious books by comparing them to the Greek originals. These corrected texts became models for the Orthodox churches using Church Slavonic language: Bulgaria, Serbia, Romania, and Ukraine. Gregory Tsamblak, his biographer, compared Euthymius' work to that of Moses and Egyptian king Ptolemy I. In 1375, following the death of Patriarch Joanicius, Euthymius was elected to become his successor. A supporter of asceticism, Euthymius aimed to persecute heresies and moral decay. Euthymius became a prominent figure in the Orthodox world and a number of metropolitans and hegumens addressed him to interpret theological matters. There are 15 known works by Euthymius, including liturgical books, laudatory works, passionals and epistles. Among his literary disciples are Gregory Tsamblak, Metropolitan of Kiev; Cyprian, Metropolitan of Moscow; Joasaph of Bdin and Constantine of Kostenets.
Establishment of Tarnovo Literary School and language reform
During the time of patriarch Theodosius of Tarnovo Euthymius founded and ran the Tarnovo literary school, which was to quickly become an important cultural center of the Slavic Christian world. Euthymius initiated a language reform in Old Bulgarian that was widely influential to the standardized literary languages of Serbia, Walachia, Moldova, and the Ukrainian principalities. Partial list of works: Hagiographies “Hagiography of St. Ivan of Rila” “Hagiography of St. Ilarion Maglenski” “Hagiography of St. Philothea Temnishka” “Hagiography of St. Petka of Tarnovo” Praises “Praise for Mikhail Warrior” “Praise for Ioan Polivotski” “Praise for St. Nedelya” “Praise for St. Constantine and Helena” Letters “Letter to Cyprian" “Letter to metropolitan Arsenius” “Letter to Nikodim – monk of Tismana”
In the spring of 1393 the son of OttomanSultan Bayezid I, Suleyman Çelebi, laid siege to the Bulgarian capital Tarnovo with his sizable forces. With Tsar Ivan Shishman out of the city, Euthymius was the one entrusted with the defense of Tarnovo. After a three-month siege on 17 July 1393, the Ottomans captured the capital despite its ferocious resistance; Gregory Tsamblak several years later suggested the conquest was due to treason from one of the non-Christian neighborhoods of Tarnovo. Joasaph of Bdin, Metropolitan of Vidin, a contemporary of the event, described it as follows: "A great Muslim invasion happened and total destruction was done with this city and its surroundings." According to Gregory Tsamblak, churches were turned into mosques, priests were expelled and substituted with "teachers of shamelessness." 110 noted citizens of Tarnovo and boyars were massacred, but Patriarch Euthymius was reprieved and sent into exile in the theme of Macedonia, possibly in the Bachkovo Monastery. He is supposed to have died there in 1402–1404. The Tarnovo Patriarchate thereupon ceased to exist as the Bulgarian church lost its independence and became subordinate to the Patriarchate of Constantinople until 1870. Patriarch Euthymius has been canonized and his memory is honored on the same day as that of his namesake Euthymius the Great, 20 January.
