Leo, the bishop, to Theodosius ever Augustus.
In all your piously expressed letters amid the anxieties, which we suffer for the Faith, you have afforded us hope of security by supporting the Council of Nicaea so loyally as not to allow the priests of the Lord to budge from it, as you have often written us already. But lest I should seem to have done anything prejudicial to the catholic defence, I thought nothing rash on either side ought meanwhile to be written back on the ordination of him who has begun to preside over the church of Constantinople, and this not through want of loving interest, but waiting for the catholic Truth to be made clear. And I beg your clemency to bear this with equanimity that when he has proved himself such as we desire towards the catholic Faith, we may the more fully and safely rejoice over his sincerity. But that no evil suspicion may assail him about our disposition towards him, I remove all occasion of difficulty, and demand nothing which may seem either hard or controvertible but make an invitation which no catholic would decline. For they are well known and renowned throughout the world, who before our time have shone in preaching the catholic Truth whether in the Greek or the Latin tongue, to whose learning and teaching some even of our own day have recourse, and from whose writings a uniform and manifold statement of doctrine is produced: which, as it has pulled down the heresy of Nestorius, so has it cut off this error too which is now sprouting out again. Let him then read again what is the belief on the Lord's Incarnation which the holy fathers guarded and has always been similarly preached,and when he has perceived that the letter of Cyril of holy memory, bishop of Alexandria, agrees with the view of those who preceded him [wherein he wished to correct and cure Nestorius, refuting his wrong statements and setting out more clearly the Faith as defined at Nicaea, and which was sent by him and placed in the library of the Apostolic See1 ], let him further reconsider the proceedings of the Ephesian Synod2 wherein the testimonies of catholic priests on the Lord's Incarnation are inserted and maintained by Cyril of holy memory. Let him not scorn also to read my letter3 over, which he will find to agree throughout with the pious belief of the fathers. And when he has realized that that is required and desired from him which shall serve the same good end, let him give his hearty assent to the judgment of the catholics, so that in the presence of all the clergy and the whole people he may without any reservation declare his sincere acknowledgment of the common Faith, to be communicated to the Apostolic See and all the Lord's priests and churches, and thus the world being at peace through the one Faith, we may all be able to say what the angels sang at the Saviour's birth of the Virgin Mary, "Glory in the highest to God and on earth peace to men of good will4 ."
But because both we and our blessed fathers, whose teaching we revere and follow, are in concord on the one Faith, as the bishops of all the provinces attest, let your clemency's most devout faith see to it that such a document as is due may reach us as soon as may be from the bishop of Constantinople, as from an approved and catholic priest, that is, openly and distinctly affirming that he will separate from his communion any one who believes or maintains any other view about the Incarnation of the Word of God than my statement and that of all catholics lays down, that we may fairly be able to bestow on him brotherly love in Christ. And that swifter and fuller effect, God aiding us, may be given through your clemency's faith to our wholesome desires, I have sent to your piety my brethren and fellow-bishops Abundius and Asterius, together with Basilius and Senator presbyters, whose devotion is well proved to me, through whom, when they have displayed the instructions which we have sent, you may be able properly to apprehend what is the standard of our faith, so that, if the bishop of Constantinople gives his hearty assent to the same confession, we may securely, as is due, rejoice over the peace of the Church and no ambiguity may seem to lurk behind which may trouble us with perhaps ungrounded suspicions. But if any dissent from the purity of our Faith and from the authority of the Fathers, the Synod which has met at Rome for that purpose joins with me in asking your clemency to permit a universal council within the limits of Italy; so that, if all those come together in one place who have fallen either through ignorance or through fear, measures may be taken to correct and cure them, and no one any longer may be allowed to quote the Synod of Niches in a way which shall prove him opposed to its Faith; since it will be of advantage both to the whole Church and to your rule, if one God, one Faith and one mystery of man's Salvation, be held by the one confession of the whole world.
Dated 17th July in the consulship of the illustrious Valentinianus for the seventh time) and Avienus (450).