There in some controversy as to whether St. Peter's chains were brought from Jerusalem by Eudoxia in 439, or by some travellers sent to the East in search of them by the martyr St. Balbina and her father, St. Quirinus, in 116. Gerbet defends the latter opinion and says St. Balbina gave them to Theodora, sister of St. Hermes, martyr, Prefect of Rome, from whom they passed into the hands of Pope St. Alexander I (108-117). St. Bede the Venerable, writing in the seventh century, speaks of the chains in connection with St. Balbina and St. Alexander.

Such was the reverence paid to these chains in the fifth and sixth centuries, that filings of them were considered precious relics suitable for kings and patriarchs, these filings being usually enclosed in a gold cross or key. Such a relic was sent by Pope St. Hormisdas to the Emperor Justinian; by St. Gregory to King Childebert, to Theoctista, sister of the Emperor Mauritius, to Anastasius, Patriarch of Antioch, and others; by Pope Vitalian to Oswy of Northumbria; by St. Leo III to Charlemagne; by St. Gregory VII to Alphonsus, King of Castile. These crosses and keys were often worn around the neck as a preservative against dangers, spiritual and temporal.

St. John Chrysostom's words on St. Paul's chains apply equally to St. Peter's: "No glittering diadem so adorns the head as a chain borne for Christ. Were the choice offered me either of heaven or of this chain (suffered for Christ), I would take the chain. If I might have stood with the angels above, near the throne of God, or have been bound with Paul, I should have preferred the dungeon. Had you rather have been the angel loosing Peter, or Peter in chains? I would rather have been Peter. This gift of chains is something greater than power to stop the sun, to move the world, or to command the devils" (Homil. 8, in Ephes iii. I.).

http://www.catholicculture.org/culture/liturgicalyear/calendar/day.cfm?date=2013-08-01