The council that moved from Ferrara to Florence in 1439 was the most serious attempt ever made to reunite the Latin and Greek churches. The Byzantine emperor came in person with his patriarch and a large delegation, because Constantinople needed western military help against the Ottomans, and the sessions worked through the points of difference: the addition of the filioque to the creed, the existence of purgatory, the use of unleavened bread in the eucharist, and the authority of the pope. A decree of union was signed in July.
It did not hold. Mark of Ephesus refused to sign at all. The patriarch died in Florence during the council. When the delegation returned home the union was rejected by most of the clergy and by the population, and the saying that it would be better to see the Turkish turban in the city than the Latin mitre belongs to that mood. Constantinople fell fourteen years later.
The council's other consequence was intellectual. The Greek delegation included men steeped in a philosophical tradition Latin Europe had lost, and one of them, Gemistos Plethon, lectured in Florence on the differences between Plato and Aristotle. Cosimo de' Medici heard him. Bessarion, who signed the union and became a cardinal, spent the rest of his life gathering Greek manuscripts and left his library to Venice. The immediate result in Florence was a decision to have Plato translated into Latin in full, which is where the next article begins.