(Found in Migne, Pat. Lat., Tom. LXXXVII., col. 1247 et seqq.; and Labbe and Cossart, Concilia, Tom. VI., col. 1071 et seqq.)
A copy of the letter sent by the holy and Ecumenical Sixth Council to Agatho, the most blessed and most holy pope of Old Rome.
The holy and ecumenical council which by the grace of God and the pious sanction of the most pious and faithful Constantine, the great Emperor, has been gathered together in this God-preserved and royal city, Constantinople, the new Rome, in the Secretum of the imperial (qeiou, sacri) palace called Trullus, to the most holy and most blessed pope of Old Rome, Agatho, health in the Lord.
Serious illnesses call for greater helps, as you know, most blessed [father]; and therefore Christ our true God, who is the creator and governing power of all things, gave a wise physician, namely your God-honoured sanctity, to drive away by force the contagion of heretical pestilence by the remedies of orthodoxy, and to give the strength of health to the members of the church. Therefore to thee, as to the bishop of the first see of the Universal Church, we leave what must be done, since you willingly take for your standing ground the firm rock of the faith, as we know from having read your true confession in the letter sent by your fatherly beatitude to the most pious emperor: and we acknowledge that this letter was divinely written (perscriptas) as by the Chief of the Apostles, and through it we have cast out the heretical sect of many errors which had recently sprung up, having been urged to making a decree by Constantine who divinely reigns, and wields a most clement sceptre. And by his help we have overthrown the error of impiety, having as it were laid siege to the nefarious doctrine of the heretics. And then tearing to pieces the foundations of their execrable heresy, and attacking them with spiritual and paternal arms, and confounding their tongues that they might not speak consistently with each other, we overturned the tower built up by these followers of this most impious heresy; and we slew them with anathema, as lapsed concerning the faith and as sinners, in the morning outside the camp of the tabernacle of God, that we may express ourselves after the manner of David,(1) in accordance with the sentence already given concerning them in your letter, and their names are these: Theodore, bishop of Pharan, Sergius, Honorius, Cyrus, Paul, Pyrrhus and Peter. Moreover, in addition to these, we justly subjected to the anathema of heretics those also who live in their impiety which they have received, or, to speak more accurately, in the impiety of these God-hated persons, Apollinaris, Severus and Themestius, to wit, Macarius, who was the bishop of the great city of Antioch (and him we also stripped deservedly of his pastor's robes on account of his impenitence concerning the orthodox faith and his obstinate stubbornness), and Stephen, his disciple in craziness and his teacher in impiety, also Polychronius, who was inveterate in his heretical doctrines, thus answering to his name; and finally all those who impenitently have taught or do teach, or now hold or have held similar doctrines.
Up to now grief, sorrow, and many tears have been our portion. For we cannot laugh at the fall of our neighbours, nor exult with joy at their unbridled madness, nor have we been elated that we might fall all the more grievously because of this thing; not thus, O venerable and sacred head, have we been taught, we who hold Christ, the Lord of the universe, to be both benign and man-loving in the highest degree; for he exhorts us to be imitators of him in his priesthood so far as is possible, as becometh the good, and to obtain the pattern of his pastoral and conciliatory government. But also to true repentance the most Serene Emperor and ourselves have exhorted them in various ways, and we have conducted the whole matter with great religiousness and care. Nor have we been moved to do so for the sake of gain, nor by hatred, as you can easily see from what things have been done in each session, and related in the minutes, which are herewith sent to your blessedness: and you will understand from your holiness's vicars, Theodore and George, presbyters beloved of God, and from John, the most religious deacon, and from Constantine, the most venerable sub-deacon, all of them your spiritual children and our well-loved brethren. So too you will hear the same things from those sent by your holy synod, the holy bishops who rightly and uprightly, in accordance with your discipline, decreed with us in the first chapter of the faith.
Thus, illuminated by the Holy Spirit, and instructed by your doctrine, we have cast forth the vile doctrines of impiety, making smooth the right path of orthodoxy, being in every way encouraged and helped in so doing by the wisdom and power of our most pious and serene Emperor Constantine. And then one of our number, the most holy praesul of this reigning Constantinople, in the first place assenting to the orthodox compositions sent by you to the most pious emperor as in all respects agreeable to the teaching of the approved Fathers and of the God-instructed Fathers, and of the holy five universal councils, we all, by the help of Christ our God, easily accomplished what we were striving after. For as God was the mover, so God also he crowned our council.
Thereupon, therefore, the grace of the Holy Spirit shone upon us, displaying his power, through your assiduous prayers, for the uprooting of all weeds and every tree which brought not forth good fruit, and giving command that they should be consumed by fire. And we all agree both in heart and tongue, and hand, and have put forth, by the assistance of the life-giving Spirit, a definition, clean from all error, certain, and infallible; not `removing the ancient landmarks, as it is written (God forbid!), but remaining steadfast in the testimonies and authority of the holy and approved fathers, and defining that, as of two and in two natures (to wit, the divinity and the humanity) of which he is composed and in which he exists, Christ our true God is preached by us, and is glorified inseparably, unchangeably, unconfusedly, and undividedly; just so also we predicate of him two natural operations, undividedly, incontrovertibly, unconfusedly, inseparably, as has been declared in our synodal definition. These decrees the majesty of our God-copying Emperor assented to, and subscribed them with his own hand. And, as has been said, we rejected and condemned that most impious and unsubstantial heresy which affirmed but one will and one operation in the incarnate Christ our true God, and by so doing we have pressed sore upon the crowd who confound and who divide, and have extinguished the inflamed storm of other heresies, but we have set forth clearly with you the shining light of the orthodox faith, and we pray your paternal sanctity to confirm our decree by your honourable rescript; through which we confide in good hope in Christ that his merciful kindness will grant freely to the Roman State, committed to the care of our most clement Emperor, stability; and will adorn with daily yokes and victories his most serene elemency; and that in addition to the good things he has here bestowed upon us, he will set your God-honoured holiness before his tremendous tribunal as one who has sincerely confessed the true faith, preserving it unsullied and keeping good ward over the orthodox flocks committed to him by God.'
We and all who are with us salute all the brethren in Christ who are with your blessedness.