Orthodox Christian belief has it that Jesus ascended bodily into Heaven at the end of his earthly life. This would mean that his foreskin (removed at his circumcision, as with all other Jewish boys) would be one of the few physical remainders of Jesus left behind on Earth. Indeed, there seems to have been some short-lived theological arguments as to whether Jesus can really be said to have ascended wholly into Heaven if this part of his body was actually missing; consensus was that his foreskin was no more an obstacle to this than the hair and fingernails that he had cut throughout his life.
The abbey of Charroux claimed to own the Holy Foreskin during the Middle Ages. It was said to have been presented to the monks by none other than Charlemagne, who in turn claimed (as the legend has it) that it had been brought to him by an angel (although another version of the story says it was a wedding gift from Empress Irene of the Byzantine Empire). In the early 12th century, it was taken in procession to Rome where it was presented before Pope Innocent III, who was asked to rule on its authenticity. The Pope declined the opportunity. Later, however, Pope Clement VII declared it to be a true relic, and granted an indulgence to pilgrims who went to visit it. At some point, however, the relic went missing, and remained lost until 1856 when a workman repairing the abbey claimed to have found a reliquary hidden inside a wall, containing the missing foreskin.
The abbey church of Coulombs in the diocese of Chartres, France was another medieval claimant. One story says that when Catherine of Valois was pregnant in 1421, her husband, King Henry V of England, sent for the Holy Prepuce. It was believed that the sweet scent that the relic was supposed to give off would ensure an easy and safe childbirth. According to this legend, it did its job so well that Henry was reluctant to return it after the birth of the child (the future King Henry VI of England).
The authenticity of the Holy Foreskin claimed by St. John Lateran in Rome is said to have been proven in 1527 when the troops of Holy Roman Emperor Charles V sacked Rome. The relic fell into their hands for a time, and was allegedly put to the test by bringing a virgin girl before it, whereupon the foreskin expanded!
The last of these is worthy of special mention as the reliquary containing the Holy Foreskin was paraded through the streets of this Italian village as recently as 1983 on the Feast of the Circumcision (marked by the Catholic church around the world on January 1 each year). The practice ended, however, when thieves stole the jewel-encrusted case, contents and all.
Over the last century or so, the emphasis placed on relics by the Catholic church has declined markedly, with many relics with long traditions being relegated to "pious legend" by the Vatican. Interest in the Holy Foreskins has been specifically downplayed, with the observation in 1900 that these particular relics encouraged irreverent curiosity.
Apart from its physical importance as a relic, the Holy Foreskin appears in a famous vision of Saint Catherine of Siena. In the vision, Christ mystically marries her, and his amputated foreskin is given to her as a wedding ring. During the late 17th century, Catholic scholar and theologian Leo Allatius in De Praeputio Domini Nostri Jesu Christi Diatriba ("Discussion concerning the Prepuce of our Lord Jesus Christ") speculated that the Holy Foreskin may have ascended into Heaven at the same time as Jesus himself and might have become the rings of Saturn then-recently observed.
Assuming that it is possible that one of these foreskins is in fact Jesus Christ's, its preservation raises the possibility of cloning when that technology is perfected for humans.