I. Anatolius with Leo's delegates is to settle the question of the receiving back of those who had temporarily gone astray after Eutyches.
Leo, the bishop, to the bishop Anatolius.
Although I hope, beloved, you are devoted to every good work, yet that your activity may be rendered the more effective, it was needful and fitting to dispatch my brothers Lucentius the bishop and Basil the presbyter, as we promised, to ally themselves with you, beloved, that nothing may be done either indecisively or lazily in matters, which concern the welfare of the universal Church; for as long as you are on the spot, to whom we have entrusted the carrying out of our will, all things can be conducted with such moderation that the claims of neither kindness nor justice may be neglected, but without the accepting of persons, the Divine judgment may be considered in everything. But that this may be properly observed and guarded, the integrity of the Catholic Faith must first of all be preserved, and, because in all cases “narrow” and steep “is the way that leads unto life,” there must be no deviation from its track, either to the right hand or to the left. And because the evangelical and Apostolic Faith has to combat all errors, on the one side casting down Nestorius, on the other crushing Eutyches and his accomplices, remember the need of observing this rule, that all those who in that synod, which cannot, and does not deserve to have the name of Synod, and in which Dioscorus displayed his bad feeling, and Juvenal his ignorance, grieve as we learn from your account, beloved, that they were conquered by fear, and being overcome with terror, were able to be forced to assent to that iniquitous judgment, and who now desire to obtain Catholic communion, are to receive the peace of the brethren after due assurance of repentance, on condition that in no doubtful terms they anathematize, execrate and condemn Eutyches and his dogma and his adherents.
Source: Letters (New Advent)