The very government also of your kingdom in relation to your subjects ought to be tempered with moderation, lest power steal upon your mind. For a kingdom is ruled well when the glory of reigning does not dominate the disposition. Care also is to be taken that wrath creep not in, lest whatever is lawful to be done be done too hastily. For wrath, even when it prosecutes the faults of delinquents, ought not to go before the mind as a mistress, but attend as a handmaid behind the back of reason, that it may come to the front when bidden. For, if once it begins to have possession of the mind, it accounts as just what it does cruelly. For hence it is written, The wrath of man works not the righteousness of God. Hence again it is said, Let every man be swift to hear, but slow to speak, and slow to wrath (Ib. 19). However I doubt not that under the guidance of God you observe all these things. Still, now that an opportunity of admonition has arisen, I join myself furtively to your good deeds, so that what you do though not admonished you may not do alone, having an admonisher to boot. Now may Almighty God protect you in all your doings by the stretching out of His heavenly arm, and grant you prosperity in the present life, and after a course of many years eternal joys.
We have sent you a small key from the most sacred body of the blessed apostle Peter to convey his blessing, containing iron from his chains, that what had bound his neck for martyrdom may loose yours from all sins. We have given also to the bearer of these presents, to be offered to you, a cross in which there is some of the wood of the Lord's cross, and hairs of the blessed John the Baptist, from which you may ever have the succour of our Saviour through the intercession of His forerunner.
Moreover we have sent to our most reverend brother and fellow bishop Leander a pallium from the See of the blessed Apostle Peter, which we owe both to ancient custom, and to your character, and to his goodness and gravity.
A long time ago, when a certain Neapolitan youth came hither, your to me most sweet Excellency had thought fit to charge me to write to the most pious Emperor to the end that he might search in the record office for the treaties that had formerly been concluded with the prince Justinian of pious memory as to the claims of your kingdom, so as to gather from them what he should observe with regard to you. But there were two things seriously in the way of my doing this. One was that the record-office in the time of the aforesaid prince Justinian of pious memory had been so burnt by a fire which had crept in suddenly that hardly any paper of his times remained. The other was that, as no one need be told, you ought to look in your own archives for the documents that are against you, and produce these instead of my doing so. Wherefore I exhort your Excellency to arrange matters suitably to your character, and carefully to carry out whatever makes for peace, that the times of your reign may be memorable with great praise through many courses of years. Furthermore, we have sent you another key from the most sacred body of the blessed apostle Peter, which, being laid up with due honour, may multiply with blessing whatever it may find you enjoying.
Source: Register of Letters (New Advent)