Such was the veneration for the relics of the Holy Apostles Peter and Paul, deposited at Rome, that the popes themselves dared not presume to approach, touch, separate, or give away part of the precious remains of their bodies. This was out of fear, since the belief in Rome was that if you presume to touch the bodies of the Saints, punishment will follow, and they were shocked that the Greeks often touched the bodies of the saints. Pope Gregory the Great explains this fully in Registrum Epistolarum, Bk. 4, Epist. 30, which is a letter to Empress Constantina, who requested the head of Saint Paul or another part of his body be brought to Constantinople for a church being erected in his honor, and to which he replied that this could not be done, for the bodies of Peter and Paul gleamed with miracles and terrors, and there were stories of people dying when they approached them. Instead, he offered her the following:
"But since so religious a desire of my most serene lady ought not to be wholly unsatisfied, I will make haste to transmit to you some portion of the chains which Saint Peter the apostle himself bore on his neck and his hands, from which many miracles are displayed among the people; if at least I should succeed in removing it by filing. For, while many come frequently to seek a blessing from these same chains, in the hope of receiving a little part of the filings, a priest attends with a file, and in the case of some seekers a portion comes off so quickly from these chains that there is no delay; but in the case of other seekers the file is drawn for long over the chains, and yet nothing can be got from them."
Pope Gregory therefore offered her a filing from the chain of the Apostle Peter instead of the head of Saint Paul and a napkin that was too close to his body to be touched. These filings were offered to the faithful in general upon request, and there are many instances of the popes themselves giving away these filings. When Emperor Justinian asked the representatives of Pope Hormisdas for relics of Saint Laurence, the response was decidedly cool, so he settled for something from the chains of Saint Peter and the gridiron upon which Saint Laurence was roasted. Again, when Patriarch Eulogios of Constantinople informed Pope Pelagius I that he would very much like some relics of Saint Peter, the pope responded by sending filings from his chains and a tunic that had been left for three days in the interior of Peter's tomb.
The popes were accustomed to send the filings of these chains as precious relics, to devout royals, and they were often instruments of miracles. The pope himself rasped off these filings, which he enclosed in a cross or in a golden key, as appears from Pope Gregory the Great, who says in his letter to King Childebert, to whom he sent one of these keys, "Moreover we have sent to your Excellency Saint Peter's keys, containing a portion of his chains, to protect you from all evils, when hung on your neck" (Registrum Epistolarum, Bk. 6, Epist. 6). He gave the same to Bishop Columbus: "I have transmitted to you for a blessing keys of the blessed Peter, in which something from his chains is included" (Registrum Epistolarum, Bk. 3, Epist. 48). And to Edilbert, King of the Angli, the same was given: "I have sent you some small presents, which to you will not be small, when received by you as of the benediction of the blessed Apostle Peter" (Registrum Epistolarum, Bk. 11, Epist. 66).
To the Patrician Theoctista the pope even relates a miracle from one of these keys:
"I send you, as a blessing from Saint Peter the apostle, a key from his most sacred body; with respect to which key the miracle has been wrought which I now relate. A certain Lombard, having found it on his entrance into a city in the parts beyond the Po, and, paying no regard to it as Saint Peter's key, but wishing to make something of it for himself in that he saw it to be of gold, took out a knife to cut it. But presently seized by a spirit, he plunged the knife wherewith he had thought to cut it into his own throat, and in the same hour fell down dead. And when Autharith, king of the Lombards , and many others belonging to him came to the place, and he who had stabbed himself was lying apart in one place dead, and this key on the ground in another, exceeding fear came upon all, so that no one ventured to lift this same key from the ground. Then a certain Lombard who was a Catholic, and known to be given to prayer and almsgiving, Minulf by name, was called, and himself lifted it from the ground. But Autharith, in consideration of this miracle, made another golden key, and sent it along with this to my predecessor of holy memory, declaring what kind of miracle had through it occurred. I have taken thought, then, to send your Excellence this key, through which Almighty God cut off a proud and faithless man, that through it you who fear and love Him may be enabled to have both present and eternal welfare" (Registrum Epistolarum, Bk. 7, Epist. 26).
With a prayer that the chain which bound the neck of the Apostle Peter may loose him of his sins, Pope Gregory sent Ex-Consul Leontius a key as well: "We send you, as a blessing from Saint Peter, Prince of the apostles, a key of his most sacred sepulchre, in which is inserted a blessing from his chains, that what bound his neck for martyrdom may loose yours from all sins" (Registrum Epistolarum, Bk. 8, Epist. 35).
The same was gifted with a similar prayer to Rechared, King of the Visigoths, though he gave him also another key to enrich his blessings: "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... 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" (Registrum Epistolarum, Bk. 9, Epist. 122).
To heal Patriarch Eulogios of Alexandria from an ailment of the eyes, Pope Gregory sent a cross with filings of the chain to be applied to his eyes for healing: "We have sent you a small cross, in which is inserted a blessing from the chains of your lovers the apostles Saint Peter and Saint Paul; and let this be continually applied to your eyes, seeing that many miracles have been wont to be wrought through this same blessing" (Registrum Epistolarum, Bk. 3, Epist. 42).
From these cases alone, we see that the chains of Saint Peter were widely distributed by the popes, especially by Pope Gregory the Great, for a blessing, for healing, and as an act of authority, to show that he alone held the key to the Kingdom, as a successor of the Apostle Peter.