The Council of Florence was the seventeenth ecumenical council recognized by the Catholic Church, held between 1431 and 1445. It was convened in territories under the Holy Roman Empire. Italy became a venue of a Catholic ecumenical council after a gap of about two centuries (the last ecumenical council to be held in Italy was the 4th Council of the Lateran in Rome's Lateran Palace in 1215). It was convoked in Basel as the Council of Basel by Pope Martin V shortly before his death in February 1431 and took place in the context of the Hussite Wars in Bohemia and the rise of the Ottoman Empire. At stake was the greater conflict between the conciliar movement and the principle of papal supremacy.
The Council entered a second phase after Emperor Sigismund's death in 1437. Pope Eugene IV translated the Council to Ferrara on 8 January 1438, where it became the Council of Ferrara and succeeded in drawing some of the Byzantine delegates who were in attendance at Basel to Italy. Some Council members rejected the papal decree and remained at Basel: this rump Council suspended Eugene, declared him a heretic, and in November 1439 elected an antipope, Felix V.
After becoming the Council of Florence (having moved to avoid the bubonic plague in Ferrara), the Council concluded in 1445 with the promulgation of a decree of union with delegates of the Eastern Orthodox Church.
The union was not universally accepted among the Eastern Christian churches. The delegates of the Georgian Orthodox Church and the Church of Alexandria did not sign the decree of union. The Serbian Orthodox Church rejected the union and was not represented at the council. Although delegates from the Patriarchate of Jerusalem and the Patriarchate of Antioch signed the decree, their patriarchs later rejected the union, maintaining that the delegates had not been authorized to make such commitments on behalf of their churches.
The union also met strong opposition in Constantinople, where the overwhelming majority of both clergy and laity rejected it, accusing the emperor and the patriarch of betrayal. As a result, the attempted resolution of the Great Schism proved short-lived and failed to gain broad acceptance in the Eastern Christian world, despite representing a significant political achievement for the papacy.
In 1447, Sigismund's successor Frederick III commanded the city of Basel to expel the Council of Basel; the rump Council reconvened in Lausanne before dissolving itself in 1449.
The initial location in the Prince-Bishopric of Basel reflected the desire among parties seeking reform to meet outside territories directly controlled by the pope, the emperor or the kings of Aragon and France, whose influences the council hoped to avoid. Ambrogio Traversari attended the Council of Basel as legate of Pope Eugene IV.
Under pressure for ecclesiastical reform, Pope Martin V sanctioned a decree of the Council of Constance (9 October 1417) obliging the papacy to summon general councils periodically. At the expiration of the first term fixed by this decree, Pope Martin V complied by calling a council at Pavia. Due to an epidemic the location transferred almost at once to Siena (see Council of Siena) and disbanded, in circumstances still imperfectly known, just as it had begun to discuss the subject of reform (1424). The next council fell due at the expiration of seven years in 1431; Martin V duly convoked it for this date to the town of Basel and selected to preside over it the cardinal Julian Cesarini, a well-respected prelate. Martin himself, however, died before the opening of the synod.
The Council was seated on 14 December 1431, at a period when the conciliar movement was strong and the authority of the papacy weak. The Council at Basel opened with only a few bishops and abbots attending, but it grew rapidly and to make its numbers greater gave the lower orders a majority over the bishops. It adopted an anti-papal attitude, proclaimed the superiority of the Council over the Pope, and prescribed an oath to be taken by each new Pope. On 18 December Martin's successor, Pope Eugene IV, tried to dissolve it and open a new council on Italian soil at Bologna, but he was overruled.
The council was held in the Cathedral of Basel, where benches were placed for the 400 and more members, and general congregations were held either in the cathedral or in its chapter house. The clerks of ceremonies were Enea Silvio Piccolomini and Michel Brunout.
Sigismund, King of Hungary and titular King of Bohemia, had been defeated at the Battle of Domažlice in the fifth crusade against the Hussites in August 1431. Under his sponsorship, the Council negotiated a peace with the Calixtine faction of the Hussites in January 1433. Pope Eugene acknowledged the council in May and crowned Sigismund Holy Roman Emperor on 31 May 1433. The divided Hussites were defeated in May 1434. In June 1434, the pope had to flee a revolt in Rome and began a ten-year exile in Florence.
Replacement by the Council of Florence
In 1438, Pope Eugene convened a new council at Ferrara, which however was transferred to Florence in 1439 because of the danger of plague at Ferrara and because Florence had agreed, against future payment, to finance the Council.
Most of the original Council moved from Basel to Ferrara in 1438. Some remained at Basel, still claiming to be the Council. They elected Amadeus VIII, Duke of Savoy, as Pope Felix V. He is considered an antipope, and was the only claimant to the papal throne who ever took the Basel oath. Driven out of Basel in 1448, they moved to Lausanne. In 1449, Felix V resigned and the rump Council formally closed.
The Council had meanwhile successfully negotiated reunification with several Eastern Churches, reaching agreements on such matters as the Western insertion of the phrase "Filioque" to the Nicene-Constantinopolitan Creed, the definition and number of the sacraments, and the doctrine of Purgatory. Another key issue was papal supremacy, which involved the universal and supreme jurisdiction of the Bishop of Rome over the whole Church, including the national churches of the East (Serbian, Byzantine, Moldo-Wallachian, Bulgarian, Russian, Georgian, Armenian, Coptic, Syriac etc.), and secular matters such as the promise of military assistance against the Ottoman Empire.
On 6 July 1439, the union was proclaimed (in both Latin and Greek) in the document Laetentur Caeli ("Let the Heavens Rejoice"), which was signed by Pope Eugene IV and by the Byzantine Emperor John VIII Palaiologos. All but one of the bishops were present. Some Greek bishops, perhaps feeling political pressure from the Byzantine Emperor, reluctantly accepted the decrees of the Council. Other Eastern bishops did so out of sincere conviction, such as Isidore of Kiev, who subsequently suffered greatly for it. Among the Eastern bishops, Mark of Ephesus refused to accept the union, becoming the leader of the opposition back in Byzantium. A representative of the Georgian Orthodox Church, Gregory, Metropolitan of Tbilisi, who attended the council on behalf of David III, Catholicos-Patriarch of Georgia, shared the position of Mark of Ephesus and likewise refused to sign the decree of union. Bishop Isaiah of Stavropol likewise opposed the union and fled from Florence.
The Serbian Patriarch, Teofan I, did not even attend the council. The only Russian prelate present, Avraamy of Suzdal, signed the union, but Russian sources claimed that this was under duress from Metropolitan Isidore. The Russian Orthodox Church, upon learning of the union, angrily rejected it and ousted any prelate who was even remotely sympathetic to it, declaring itself autocephalous (i.e., autonomous), with subsequent Russian sources portraying the actions of Grand Prince Vasily II of Moscow as protecting the purity of the faith.
Despite the religious union, Western military assistance to Byzantium was ultimately insufficient, and the fall of Constantinople occurred in May 1453. The Council declared the Basel group heretics and excommunicated them, and affirmed the superiority of the Pope over the Councils in the bull Etsi non dubitemus of 20 April 1441.