Whereas we have heard that in some places in the hymn Trisagion there is added after “Holy and Immortal,” “Who was crucified for us, have mercy upon us,” and since this as being alien to piety was by the ancient and holy Fathers cast out of the hymn, as also the violent heretics who inserted these new words were cast out of the Church; we also, confirming the things which were formerly piously established by our holy Fathers, anathematize those who after this present decree allow in church this or any other addition to the most sacred hymn; but if indeed he who has transgressed is of the sacerdotal order, we command that he be deprived of his priestly dignity, but if he be a layman or monk let him be cut off.
Ancient Epitome of Canon LXXXI.
Whoever adds to the hymn Trisagion these words “Who wast crucified” shall be deemed heterodox.
The addition of the phrase condemned by this canon was probably made first by Peter Fullo, and although indeed it was capable of a good meaning, if the whole hymn was understood as being addressed to Christ, and although this was admitted by very many of the orthodox, yet as it was chiefly used by the Monophysites and with an undoubtedly heretical intention, it was finally ousted from this p. 401 position and its adherents were styled Theopaschites. From all this it came about that by 518 it was a source of disagreement among the Catholics, some affirming the expression, as looked at by itself, to be a touchstone of orthodoxy. The Emperor Justinian tried to have it approved by Pope Hormisdas, but unsuccessfully, the pontiff only declaring that it was unnecessary, and even dangerous. Fulgentius of Ruspe and Dionysius Exiguus had declared it orthodox. Pope John II. almost came to the point of approving the phrase “one of the Trinity suffered,” nor did his successor Agapetus I. speak any more definitely on the point, but the Fifth Ecumenical Council directly approved the formula.
But this, of course, did not touch the point of its introduction into the Trisagion or, more accurately, of the introduction of the words “who was crucified for us.”
It should have been noted that at a Home Synod in 478, Peter Fullo had been deposed for the insertion of this clause, because he intended to imply that the true God had suffered death upon the cross. This sentence was a confirmation of one already pronounced against him by a synod held at Antioch which had raised a man, Stephen by name, to its episcopal throne.
Such is the history of a matter which, while it seemed at first as of little moment, yet for many years was a source of trouble in the Church. (Vide Hefele, History of the Councils, Vol. III., pp. 454, 457; Vol. IV., p. 26.)