The struggle between these two systems continued well into the 10th century; and, though episcopalism was not infrequently proscribed by the curia, it still survived, and till the year 1870 could boast that no ecumenical council had ventured to condemn it.
Convoked an ecumenical council at Ephesus, to which Celestine sent his legates.
At the great ecumenical council held at Constantinople in 381, he was a conspicuous champion of the orthodox faith; according to Nicephorus, indeed, the additions made to the Nicene creed were entirely due to his suggestion, but this statement is of doubtful authority.
Thus, in the third, fourth and fifth general sessions it was enacted, with characteristic precipitation, that an ecumenical council could not be dissolved or set aside by the pope, without its consent: the corollary to which was, that the present council, notwithstanding the flight of John XXIII., continued to exist in the full possession of its powers, and that, in matters pertaining to belief and the eradication of schism, all men - even the pope - were bound to obey the general council, whose authority extended over all Christians, including the pope himself.
This doctrine, rather political than theological, was a survival of the errors which had come into being after the Great Schism, and especially at the council of Constance; its object was to put the Church above its head, as the council of Constance had put the ecumenical council above the pope, as though the council could be ecumenical without its head.
But these declarations as to the superiority of an ecumenical council never attained legal validity, in spite of their defence by Pierre d'Ailly and Gerson.
As a result the ecumenical council came into existence especially for the purpose of settling disputed questions of doctrine, and giving to the collective episcopate the opportunity to express its voice in a final and official way.
With the addition of the twenty-two canons of the ecumenical council of Nicaea (787), this will give us the whole contents of the official collection of the Greek Church; since then it has remained unchanged.
Emanating from an assembly without a head, which could not possibly be an ecumenical council without the assent of one of the popes (of whom one was necessarily the legitimate pope) - enacted, in opposition to the cardinals, by a majority of persons for the most part unqualified, and in a fashion which was thus distinctly different from that of the old of John councils - they can only be regarded as a coup de XXIII.
Under the Empire the ecumenical council had been looked upon as the highest representative organ of the Catholic Church; but the earlier centuries of the middle ages witnessed the convocation of no ecumenical councils.