I. He wishes his assent to the acts of Chalcedon to be widely known.
Leo to Julian the bishop.
How watchfully and how devotedly you guard the Catholic Faith, brother, the tenor of your letter shows, and my anxiety is greatly relieved by the information it contains; supplemented as it is by the most religious piety of our religious Emperor, which is clearly shown to be prepared by the Lord for the confirmation of the whole Church; so that, while Christian princes act for the Faith with holy zeal, the priests of the Lord may confidently pray for their realm.
What therefore our most clement Emperor deemed needful I have willingly complied with, by sending letters to all the brethren who were present at the Synod of Chalcedon, in which to show that I approved of what was resolved upon by our holy brethren about the Rule of Faith; on their account to wit, who in order to cloke their own treachery, pretend to consider invalid or doubtful such conciliar ordinances as are not ratified by my assent: albeit, after the return of the brethren whom I had sent in my stead, I dispatched a letter to the bishop of Constantinople; so that, if he had been minded to publish it, abundant proof might have been furnished thereby how gladly I approved of what the synod had passed concerning the Faith. But, because it contained such an answer as would have run counter to his self-seeking, he preferred my acceptance of the brethren's resolutions to remain unknown, lest at the same time my reply should become known on the absolute authority of the Nicene canons. Wherefore take heed, beloved, that you warn our most gracious prince by frequent reminders that he add his words to ours and order the letter of the Apostolic See to be sent round to the priests of each single province, that hereafter no enemy of the Truth may venture to excuse himself under cover of my silence.
Source: Letters (New Advent)