Isidore of Kiev
Byzantine prelate who pushed church union and whose deposition sparked Russian autocephaly.
A supporter of union with Rome, he attended the Council of Ferrara–Florence and later proclaimed the union at Hagia Sophia. His deposition in Moscow and rejection of the union by the Russian Church contributed to the Russian Church's declaration of autocephaly in 1448.
- known_for
- Advocating union of Greek and Latin churches; metropolitan of Kiev; cardinal priest of Santi Marcellino e Pietro, later cardinal bishop of Sabina
Lore & Background
He was well-connected and had the patronage of the Palaiologos dynasty. His education likely took place in Constantinople, where he studied the scriptures, Church Fathers, and ecclesiastical law, and trained in ancient Greek. Claims that he studied alongside Italian humanists like Guarino da Verona remain unsubstantiated.
Reader's Guide
Isidore's significance lies in his role as a catalyst for the separation of the Russian Orthodox Church from Constantinople. His support for the union with Rome, formalized at the Council of Florence in 1439, was rejected by Grand Prince Vasily II and the Russian clergy. After the fall of Constantinople, he returned to Rome, where he held high offices in the Latin Church, including cardinal bishop of Sabina and Latin Patriarch of Constantinople. His legacy is that of a figure who, through his actions, inadvertently helped establish an independent Russian Orthodox Church.
Did You Know?
- Isidore was made cardinal and Apostolic Delegate for Lithuania, Livonia, Russia, and parts of Poland after the Council of Florence.
- His journey from Florence to Moscow took nearly twice as long as his journey to Ferrara.
Frequently Asked Questions
Who is Isidore of Kiev?
Isidore of Kiev was a Byzantine prelate who served as metropolitan of Kiev and became the most prominent advocate for reuniting the Greek and Latin churches under Roman authority. He was later elevated to the cardinalate, first as cardinal priest of Santi Marcellino e Pietro and then as cardinal bishop of Sabina.
What did Isidore of Kiev do at the Council of Ferrara–Florence?
He attended the council as a leading proponent of union with Rome and subsequently traveled to Constantinople to publicly proclaim the agreed-upon reunion from the pulpit of Hagia Sophia. His visible role made him the face of the 1439 Florentine decree in the Byzantine world.
How did Isidore of Kiev's story end?
Upon returning to Moscow, the Russian clergy rejected both him personally and the union he championed, resulting in his deposition. His removal, combined with the broader refusal of the Russian Church to accept the Florentine agreement, directly paved the way for Moscow's declaration of full autocephaly in 1448.
What ecclesiastical positions did Isidore of Kiev hold?
He served as metropolitan of Kiev, the senior see of the Rus' Church, and was later created a cardinal by the Pope. His cardinalate advanced from the titular church of Santi Marcellino e Pietro to the suburban see of Sabina.
Why is Isidore of Kiev considered significant in medieval church history?
He was the principal Byzantine voice pushing for an institutional East–West reunion in the fifteenth century. His deposition in Moscow and the Russian Church's outright rejection of the union he announced catalyzed the Russian Church's break from Constantinople and its 1448 autocephaly.
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