In 1054, the Pope excommunicated the patriarch and his whole Church for censuring the faith of Rome. The courtesy was solemnly returned by Constantinople against the Roman Church. Other eastern patriarchs adhered to the See of Constantinople and the rupture was complete. The sack of Constantinople by Latin Christians in the fourth crusade (thirteenth century) widened the breach. At the Council of Lyons, 1274, delegates of the Eastern Empire abjured the schism, by receiving the Nicene Creed with "filioque" in it and by swearing to conform to the Roman faith and to accept the supremacy of the Pope, but the eastern patriarchs refused to do so. When, in 1439 at the Council of Florence, the Eastern Emperor and churchmen signed a compact of reunion, they were induced to acknowledge the Pope as the "successor of Peter the chief of the apostles, and the vicar of Christ, the head of the whole Church, and father and teacher of all Christians, to whom plenary power was given by our Lord Jesus Christ to feed, rule, and govern the universal Church." Other differences were patched up. The Pope, for his part, agreed to induce the rulers of the West to go to the defence of the East against the Turks, but failed to make his promise good. The people of the East were sorely disappointed and forced the repudiation of the agreement. In 1453, however, Constantinople fell a prey to the Mohammedan Turks, and the strength of the Eastern Church was broken. In modern times, papal absolutism and eastern stagnation have prevented the reunion.[286:1]