Isidore of Kiev

John Florens | May 9, 2024

Table of Content


Isidore of Kiev (Greek, Ἰσίδωρος τοῦ Κιέβου, Russian, Исидор Киевский), also known as Isidore of Thessaloniki (Thessaloniki, Greece, 1385-Rome, April 27, 1463) was a metropolitan bishop of Kiev and All Russia, Latin patriarch of Constantinople, cardinal of the Catholic Church, humanist and theologian. He was one of the leading Eastern advocates of the reunion of the Catholic and Orthodox Churches at the Council of Florence.

Upon arriving in Constantinople he became a monk, being appointed hegumen of the monastery of St. Demetrius. He had a good command of Latin and considerable fame as a theologian, distinguished by his oratorical skills. From the early stages of his ecclesiastical career he advocated reunion with the Western Church.

At that time, the court of Constantinople was considering asking the princes of the West to rescue them after meeting with the Catholic Church, since the Ottoman Empire was already very close. In 1434, Isidore was sent to the Council of Basel by John VIII Palaeologus (1425-1448) as part of an embassy to open negotiations. Here he made a speech on the splendor of the Roman Empire in Constantinople. On his return he continued to take part in the meeting among the people of Constantinople.

In 1437, Isidore was appointed metropolitan of Kiev and all Russia by Patriarch Joseph II, under the auspices of Emperor John VIII Paleologus, to reconcile the Russian Orthodox Church with the Catholic Church and to ensure the protection of Constantinople against invaders from the Ottoman Empire. Grand Prince Basil II of Moscow received the new metropolitan with hostility. As soon as he arrived he began to form a Russian legation for the council, which had moved to Ferrara. Anyway, Isidore managed to persuade the great prince to join Catholicism for the purpose of saving the Byzantine Empire and the Orthodox Church of Constantinople. Basil II made him promise that he would return without having harmed "the rights of the Divine law and the constitution of the Holy Church".

Council of Ferrara

After Isidore received funding from Basil II, he went to Ferrara and later to Florence (papal residence at the time), where the council for the followers of Eugene IV was moved, because of an outbreak of plague in the first city, in 1439, to the continuation of the Council of Basel. Leaving Moscow, then capital of the Principality of Moscow, with the legation on September 8, 1437, and passing through Riga and Lübeck, he arrived in Ferrara on August 15, 1438. On the way he had annoyed his companions by his friendly treatment of Latin ecclesiastics. In both Ferrara and Florence, Isidore was one of the six speakers on the Byzantine side. Together with Basil Bessarion, he worked categorically for the union, never changing his mind about it. He was opposed by the Russian ambassador, Phoma (Thomas) of Tver. Finally, the agreement of union between the Eastern and Western churches was signed and Isidore returned to Muscovy, for which Siropulus and other Greek writers later accused him of perjury for the promise he had made to Basil II.

At this time, it was clear to both the Byzantine imperial court and the Ecumenical Patriarchate of Constantinople that the Byzantine Empire was surrounded and cornered by the Ottoman Turks, who controlled both the Balkans and Anatolia. Serbia and Bulgaria were Turkish vassals and the Ottomans had conquered Salonica, Isidore's hometown.

The Empire at this time was reduced to the city of Constantinople, some Aegean islands, some territory in southern Greece and some coastal cities. There were fanatical Orthodox clerics who preferred the Turks to Rome, but the Emperor, the Patriarch and many others, like Isidore, wanted to achieve the reunification of the Churches and force the sending of aid from Europe to Byzantium.

On August 15, 1438, he arrived in Ferrara (Italy) from the Principality of Moscow. Isidore, Metropolitan of Kiev and all Russia, was sent by Prince Basil II of Moscow. After a journey of 11 months, he was able to participate in the Council of Florence-Ferrara, presided over by Pope Eugene IV and the Patriarch of Constantinople. The Orthodox and Eastern Churches were fully represented at this council, and even the Byzantine Emperor John VIII Paleologus was present in person.

Isidore was not Russian, but Greek, born in Thessaloniki, and had been Metropolitan of Kiev and all Russia for barely a year. He was a humanist, intellectual and enthusiastic about the mission of uniting the Eastern and Western Churches, divided since the schism of the 11th century (which reached Russia later). The Byzantine Emperor John VIII had already employed Isidore as an ambassador to the Council of Basel in 1434.

After the council (the news reached him when he was already in Benevento), he was appointed cardinal-presbyter with the title of Saints Peter and Marcellinus (being one of the few non-Latin rite individuals at that time appointed cardinal), and papal legate for the provinces of Lithuania, Livonia, all of Russia and Galitzia (Poland).

The Council fulfilled all the conditions of an ecumenical Council. The Patriarch of Constantinople was present in person, and the Patriarchs of Antioch, Alexandria and Jerusalem, blocked by the Turks, sent their representatives with the power of decision. The Patriarch of Constantinople fell ill but had a text read decreeing the universal value of the Council and indicating that whoever refused to submit to its decisions would be excommunicated.

From a theological point of view it was clear that the discrepancies between Latins and Orthodox were absolutely minor, basically of language and ritual details. All theological clashes were resolved with good will on both sides.

As "History of the Catholic Church in Russia" (by Stanislav Kozlov-Strutinski and Pavel Parféntiev, 2014 edition in Russian, a book of 730 pages) explains, due to political and material circumstances (lack of means for further residence, the need to return as soon as possible, to protect themselves from the Turks) the discussion on the main question of the primacy of the pope was abbreviated. However, on this question, too, a consensus was reached: the Greeks admitted the supreme right of the Pope to the government of the whole Church, while retaining the traditional rights and privileges of the patriarchs of the East.

The Greeks who signed the act of union did not take it as an acceptance of "Catholicism" and abdication of "Orthodoxy": from their point of view the act stated that the Greek faith "of the Holy Fathers" and the Latin confession were the same doctrine, although expressed in different terms.

The new Patriarch of Constantinople, Gregory III Mamma, favorable to the union, explained it thus in a letter to the Prince of Kiev Aleksandr Vladimir Vladimirovich (uk:Олелелько Володимирович): "All those whom we excommunicate, they also excommunicate, and those whom we cling to, they also cling to." (Popov A. Historical literary study of the Old Russian writings against the Latins (XI-XV centuries), Moscow, 1875).

Thus, the Latin and Eastern delegates approved the bull Laetentur Caeli (en:Laetentur Caeli) of July 6, 1439, promulgating the union of the Greek and Latin Churches. Isidore, metropolitan of Kiev and all Rus, signed enthusiastically. While the others simply wrote the word "sign", he wrote "I sign with love and approval" (Kartashev A.V. Essays on the History of the Russian Church, Vol. 1, Moscow, 1991).

Return to Moscow

From Budapest, in March 1440, he issued an encyclical addressed to the Russian bishops to accept the union. But when he arrived in Moscow, at Easter 1441, and proclaimed the union of the two churches in the Dormition Cathedral of the Moscow Kremlin, he saw that the majority of the bishops, Basil II and the people would not accept it. At his first pontifical Divine Liturgy in the Dormition Cathedral Isidore carried a Latin rite crucifix at the front of the procession and named Pope Eugene IV during the prayers of the liturgy. He also read aloud the decree of unification. He delivered to Basil II a message from the Vatican, with a request for assistance to the metropolitan in his task of extending the union throughout the Principality of Moscow. Three days later, six bishops, under Basil's orders, met in a synod and deposed him. After this, he was imprisoned in the Chudov Monastery for refusing to renounce the union with heretical Rome.

On this return trip Isidore learned that the Pope had named him a cardinal (there are hardly any cases at that time of non-Latin rite cardinals) and had appointed him as his legate for Lithuania, Galicia (in Poland), Livonia (the Baltic countries) and all of Russia. It was an almost unmanageable territory.

Today, Russian Orthodox nationalism tries to disavow Isidore (who was their legitimate metropolitan and went to Italy with the approval and expenses paid by the prince) and to devalue the Council of Ferrara-Florence (where Russians, Greeks and Orthodox in general were legitimately represented).

Isidore, returning to Muscovy after the Council, sent a message to each city in his extensive metropolitan area. He did not touch on theological questions. He calls himself "Archbishop of Kiev" (thus using a Latin expression) and proclaims: "Rejoice now, all of you, for the Eastern Church and the Western Church, which were for some time divided and opposed to each other, are now united with a true union in their original unity and in peace, in an ancient unity without any fissure. Accept that holy and most holy unity and union with great joy and spiritual honor. I pray all of you in the Name of Our Lord Jesus Christ who gave us His goodness that we may have no division with the Latins; for we are all servants of the Lord God and our Savior Jesus Christ and in the name of His baptism."

Then he begs his faithful not to have divisions with the Latins, to mutually accept the sacrament of baptism, and to be able to receive the sacraments and celebrate in the temples of each confession, as well as to consider the Eucharist equally real and holy, whether with or without leavened bread "because so decided in its solemn meeting the Universal Council in the city of Florence".

One argument of the most anti-Catholic Russian Orthodox (today and in the 16th century) is that the people of Rus (the Eastern Slavic lordships that would later become Russia, Belarus and Ukraine) did not want such a union. But that is confusing Rus with Moscow and its surroundings.

Historical sources, especially the earliest ones, untouched by Muscovite influence, show that the union was received with joy at least in the great Principality of Tver (neighbor and rival of the Principality of Moscow, and therefore always with an outstretched arm toward Poland). It was also welcomed, with joy, in Lithuanian Rus.

We also know that Isidore traveled through Hungary, Poland and Lithuania, visiting different dioceses of his enormous metropolitan territory. From city to city he celebrated the Eucharist mentioning Pope Eugenius IV and no Eastern Rite prelate or local prince was indignant about it or denied Isidore metropolitan authority.

When he arrived in Kiev in 1441, Prince Aleksandr Vladimir Vladimirovich - the chronicles record - gave "his Father Isidore, Metropolitan of Kiev and All Russia" a special letter confirming his fiscal and juridical rights as a metropolitan.

Thus, in Poland, in Lithuania, in Kiev, in Tver... everywhere the Orthodox communities accepted their metropolitan and the union with the Latin Christians... until Isidore arrived in Moscow.

He arrived at Easter 1441 and proclaimed the union of the two churches in the Dormition Cathedral of the Moscow Kremlin (the same one that tourists can visit today). At his first Divine Liturgy there he carried a crucifix of the Latin rite at the front of the procession and named Pope Eugene IV during the prayers of the liturgy. He also read aloud the decree of unification. It was the same as he had done in many other cities, but on the solemnity of Easter. He delivered to the Muscovite prince, Basil II, a message from the Pope, asking him to help the metropolitan to work for the union of Christians in Russia.

Three days later, the Moscow Prince Basil II of Moscow ensured that 6 bishops gathered in a hasty local synod and deposed Isidore, the official metropolitan, appointed with Constantinople's support for the whole Rus. It was a direct case of interference of the political power in the ecclesiastical organization. It can also be said that the Muscovite prince thus imposed his anti-union will on many other peoples of Rus who did not oppose it.

They imprisoned Isidore in the Chudov Monastery, demanding that he renounce the union with Rome, which he refused to do. He was imprisoned until September 1443, two years, when he was able to escape to the neighboring Principality of Tver, and later to Lithuania and Rome. Someone must have favored his escape because he took with him his extensive library of erudite humanist, which crossed Europe and is kept today in the Vatican City.

If we review Russian Orthodox texts of 20 or 30 years after these events, we see that they accuse Isidore of serious doctrinal and theological errors and heterodoxy.

But when we review sources closer in time to the facts (for example, the so-called First Chronicle of Novgorod), we see that Isidore was first accused of absolutely minor things: praying for the Pope, using a Latin cross... he was not accused of violating the universal Orthodox canons, in Greece or in the Holy Land, but "the usages of the Russian land". Those were the minuscule excuses with which Prince Basil II and his docile bishops imprisoned their metropolitan, obviously for political reasons, and not for serious doctrinal differences.

There is an undercurrent that Kozlov-Strutinski and Parféntiev emphasize in their book: in Muscovy an exorbitant importance was given to absolutely minor ritual issues that for the educated Orthodox in Greece or in other countries were not problematic. Even in the 17th century, the rift between Orthodox and Old Believers (or Old Orthodox) was based on minor ritual issues.

These two historians recall that, shortly after breaking with Isidore, "the Russian Orthodox will turn with reproaches against the Greeks and against all non-Moscovite Christians in general, accusing them that their faith is marred by such and such ritual differences and blaming them of crossing themselves with the wrong fingers and singing Alleluia at the wrong times."

From 1458 (seventeen years after Isidore's imprisonment), Orthodox texts begin to pick up another version of the story. Metropolitan of Kiev and All Rus Jonah of Moscow (docile to Prince Basil II, opposed to unity) confronted Isidore's disciple, Metropolitan Gregory II (en:Gregory the Bulgarian) who held the title of Metropolitan of Kiev, Hálych and All Rus (Митропополит Киевский, Галицкий и всея Руси). Jonah saw to it that the texts began to accuse Isidore of theological errors. But in the Tver Principality, according to the documents, they remained "Florentine" (pro-unity) basically until that date of 1458.

Another author of texts against Isidore was Hieromonk Simeon of Suzdal, who was in fact his personal enemy. This author wants to absolve the political princes of the accusation of interference in ecclesiastical affairs and to justify the Moscow metropolis to go on its own (ignoring Constantinople), charging the inks against the one who should have been its legitimate pastor, Isidore. And things that Simeon does not say, are attributed to him or "amplified" by those who quote him in later years.

In September 1443, after two years of imprisonment, Isidore escaped to Tver and later to Lithuania and Rome. He was warmly received by the Pope in 1443. Nicholas V (1447-1455) sent him as a legate to Constantinople to prepare for the reunion of the churches there in 1452, giving him two hundred soldiers for the defense of the city. On December 12 of that year he was able to gather three hundred members of the Byzantine church for a celebration of the meeting.

He lived through the capture of the city by the Turks on May 29, 1453, escaping the massacre by dressing a dead body in his cardinal's robes. While the Turks cut off the head of the corpse and paraded it through the streets, the real cardinal was shipped to Asia Minor with many other prisoners, as a slave. He would write a description of the horrors of the siege in a letter to Nicholas V.

He escaped from captivity, or bought his freedom, and returned to Rome, where he would be named Bishop of Sabina, presumably adopting the Latin rite. Pope Pius II (1458-64) would grant him two more titles: Latin Patriarch of Constantinople and Archbishop of Cyprus, which he could not exercise in a royal jurisdiction. He was Dean of the College of Cardinals from October 8, 1461.

He died in Rome on April 27, 1463. His mortal remains rest in St. Peter's Basilica in the Vatican.


  1. Isidore of Kiev
  2. Isidoro de Kiev
  3. Encyclopedia Britannica, Isidore of Kiev, 2008, O.Ed.
  4. Мартынюк А. Новгород — Вильна — Краков — Львов: где могли встретиться в середине XV века киевский митрополит Исидор и доминиканец Иоганн Реллах? // Colloquia Russica. — 2016. — Т. 6, № 1. — С. 202. Архивировано 3 июля 2020 года.
  5. Polemis I. D. Two praises of the emperor Manuel II Palaiologos. Problems of authorship // BZ. 2010. Bd. 103. S. 699—714 (текст энкомия: S. 707—710)
  6. Kalligas H. Byzantine Monemvasia. The Sources. Monemvasia, 1990. P. 179—182
  7. ^ Greek: Ἰσίδωρος τοῦ Κιέβου, romanized: Isídōros tou Kiévou; Latin: Isidorus Kioviensis; Russian: Исидор Киевский, romanized: Isidor Kievsky; Ukrainian: Ісидор Київський, romanized: Isydor Kyivs'kyy
  8. «» (Αγγλικά) Ηνωμένες Πολιτείες Αμερικής. kiev. Ανακτήθηκε στις 17  Οκτωβρίου 2020.
  9. kiev.

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