I recently wrote a piece for Catholic World Report on the relics of the nails used in the crucifixion. Here’s a bit of it:
Spread throughout the world, in cathedrals and chapels, are perhaps three dozen rough iron nails claiming to be the nails that pierced the flesh of Christ. With so many claimants, there’s a temptation to dismiss them all as pious frauds and be done with it, but do any have a legitimate claim to authenticity? Even if they don’t, does that mean they are not relics?
Relics of the cross have a single point of origin in church history: St. Helena’s pilgrimage to the hold land (326-328). St. Ambrose tells us that she
sought the nails with which the Lord was crucified, and found them. From one nail she ordered a bridle to be made, from the other she wove a diadem. [Emphasis added] She turned the one to an ornamental, the other to a devotional, use. … She sent to her son Constantine a diadem adorned with jewels which were interwoven with the iron of the Cross and enclosed the more precious jewel of divine redemption. She sent the bridle, also. Constantine used both, and transmitted his faith to later kings. And so the beginning of the faith of the emperors is the holy relic which is upon the bridle. From that came the faith whereby persecution ended and devotion to God took its place. (Funeral Oration on The Death of Theodosius, 47)
This mention of two objects created with the nails led to an early belief that only two nails pierced the Lord, one through each hand, but the text doesn’t support this. Ambrose only accounts for the use of nails in creating two things, but that doesn’t mean there were only two nails. Naturally, there’s also the question of whether Helena did, in fact, recover the genuine nails in the Holy Land, or if helpful locals simply passed off some random ironmongery as the genuine article.