The Council of Florence

The council opened at Basel in 1431 under a mandate from Pope Martin V, who died before its first session, and continued under his successor Eugene IV. When its majority asserted that a general council held authority over the pope, a position known as conciliarism, and moved to negotiate independently with the Hussites of Bohemia, Eugene IV sought to transfer the assembly to a city under closer papal control. Using the arrival of a Byzantine delegation seeking Western aid against the Ottoman Turks as his occasion, he moved the council first to Ferrara in 1438 and then, when plague broke out and Florence offered financial support through Cosimo de' Medici, to Florence in January 1439.

There, Emperor John VIII Palaiologos, Patriarch Joseph II of Constantinople and a large delegation of Greek bishops, including Bessarion of Nicaea and Mark of Ephesus, debated the Latin and Greek churches' long disputed points: the Filioque clause added to the Latin creed, the nature of purgatory, and whether leavened or unleavened bread was proper for the Eucharist. On 6 July 1439 the bull Laetentur Caeli proclaimed a formula of union on essentially Latin terms, accepting the Filioque under an accommodating reading and affirming papal primacy. Mark of Ephesus alone among the Greek bishops present refused to sign it.

The Filioque dispute turned on a single clause added to the Latin text of the Nicene Creed centuries earlier, asserting that the Holy Spirit proceeds from the Father and the Son rather than from the Father alone, as the Greek text still read; the two churches had argued over the addition, and the authority to make it, since at least the ninth century, and Florence's formula tried to accommodate both readings as compatible rather than choosing between them.

The council did not close with the Greek union. Separate bulls extended the same formula to the Armenian Church in November 1439 and, after the assembly moved on to Rome, to the Coptic and Ethiopian churches in 1442 and to Syrian, Chaldean and Cypriot Maronite communities through 1445, so that the council's full span is usually given as 1431 to 1445 across its three phases.

None of the unions proved durable. The Florence agreement was repudiated by most of the Byzantine clergy and populace once the delegation returned home, resented as a concession bought under military necessity rather than a settled reunion, and it collapsed entirely after the Ottoman conquest of Constantinople in 1453 ended the empire that had sought it. Meanwhile the rump that remained at Basel after Eugene IV's transfer refused to disperse, declared the pope deposed, and elected its own antipope, Amadeus of Savoy, who took the name Felix V, prolonging the conciliarist crisis into the 1440s until his eventual submission. The Greek scholars who traveled to Florence for the council, Bessarion foremost among them, remained an enduring legacy of a different kind, carrying Greek manuscripts and teaching into Italy at the same moment the city's own revival of classical learning was gathering pace.

Bessarion remained in the West after the council closed, was made a Latin cardinal within the year, and spent the following decades assembling one of the era's great libraries of Greek manuscripts, later bequeathed to the Republic of Venice, a legacy that outlasted the union he had signed for by centuries.