Azymite

Indeed, this usage figures as one of the three points of contention that traditionally accounted as causes (along with the issues of Petrine supremacy and the filioque in the Niceno-Constantinopolitan Creed) of the Great Schism of 1054 between Eastern and Western churches.

Regarding the usage of the primitive Church, knowledge is so scant, and the testimonies so apparently contradictory, that many theologians have pronounced the problem incapable of definitive solution.

As a visible symbol of Catholic unity, it had been the custom to maintain Greek churches and monasteries in Rome and some of Latin Rite in Constantinople.

[3] Patriarch Michael Cerularius was responding to a concrete situation within his territory – the persecution of the Byzantine Italians in southern Italy, the closing of their churches, the prohibition of their Rite, the removal of their bishops and the imposition of the Latin unleavened bread for the Eucharist.

It was in the form of a letter addressed to John, Bishop of Trani, in Apulia, at the time subject to the Byzantine emperor, and by decree of Leo the Isaurian attached to the Eastern Patriarchate.

[3] Baronius has preserved the Latin version; Cardinal Hergenröther discovered the original Greek text: The love of God and a feeling of friendliness impelled the writers to admonish the Bishops, clergy, monks and laymen of the Franks, and the Most Reverend Pope himself, concerning their azyms and Sabbaths, which were unbecoming, as being Jewish observances and instituted by Moses.

But our Pasch is replete with joy; it elevates us from the earth to heaven even as the leaven raises and warms the bread, ...[4]This validity of the etymological reasoning with the terms artos from airo was and is disputed.

At the latter Council the Greeks admitted the Latin contention that the consecration of the elements was equally valid with leavened and unleavened bread; it was decreed that the priests of either rite should conform to the custom of their respective Church.

[3] Modern Russians have claimed for their nation the initiation of the azymes controversy; but the treatises ascribed to Leontius, Bishop of Kiev, who lived a century earlier than Cerularius, and in which all the well-known arguments of the Greeks are rehearsed, are judged to have proceeded from a later pen.