From Neolithic times, if not earlier, humans have buried revered ancestors and leaders in monumental tombs that could serve as sites for pilgrimage. In part, this was an attempt for oral cultures to remember the blessed dead. Parents could take children on pilgrimage, visiting the tombs of their ancestors, while telling the stories of their great-grandparents.
A classic example from the biblical tradition was the Cave of Machpelah in Hebron, known as the Tomb of the Patriarchs Abraham, Isaac and Jacob, and their wives (Genesis 23:17-19, 50:13), and still venerated by Jews, Christians and Muslims.
Visiting the tombs of holy men and women often became a practice not just of memorialization, but of seeking spiritual blessings and healings. The holiness of a dead saint continued to reside in his bones or relics, and could be transmitted by those who touched them.
This belief is reflected in a story from 2 Kings 13:21, where, "as (a group of Israelites) were burying a man … they spied a band of (Moabite) men; and they cast the (dead) man into the sepulchre of Elisha (in order to flee the Moabites): and when the (dead) man was let down (into the tomb), and touched the bones of Elisha, he revived, and stood up on his feet."
But what if there is no known tomb for the holy man, or if the tomb is empty? This is the problem many early Christians faced with the tomb of Jesus Christ. Since Christ is resurrected, no one can visit, see or touch his bones to receive spiritual power, blessings or healing. Visiting the empty tomb of Christ was, of course, an alternative, and the Holy Sepulcher in Jerusalem remains one of the most visited Christian shrines in the world.
Many early Christians, however, seeking physical manifestations of the spiritual reality of Christ's crucifixion, death and resurrection, unceasingly searched for artifacts or relics associated with these events. And, miraculously, they found them, or at least believed they did.
The most important relic associated with Christ was the True Cross — fragments of the wood of the cross of the crucifixion, which was "invented" (meaning "discovered") by Helena, the mother of the first Christian emperor, Constantine, in A.D. 320 in a cistern which is now a chapel in the Holy Sepulcher of Jerusalem. Small fragments of this cross can be seen in many Orthodox and Catholic churches throughout the world, notably in the Greek reliquary chapel of the Holy Sepulcher in Jerusalem, and the Santa Croce in Gerusalemme (Holy Cross of Jerusalem), one of the seven Pilgrim Churches of Rome.
The discovery of other relics associated with the last days of Christ followed over the centuries. Most famous was the Holy Grail ("cup/chalice") used by Jesus at the Last Supper. Two candidates can still be seen in the Cathedral of Valencia (Spain) and the Cathedral of Genoa (Italy) — which, of course, raises the messy problem of duplicate and forged relics. (Some 200 grails or chalices have been put forward as the original.)
According to tradition, a young woman named Veronica wiped the brow of Christ with her veil, which miraculously received the imprint of Jesus's face. The resultant relic, the Veil of Veronica — whose name is an anagram for "vera icon" ("true image") — is in St. Peter's Basilica in Rome and has been reproduced in numerous paintings and icons.
The Crown of Thorns was placed on the head of Jesus as part of the torture that accompanied his trial (Matthew 27:29). A relic claiming to be that crown was located in Constantinople for centuries; individual thorns were plucked from it and given as gifts to medieval Christian rulers. Louis IX of France eventually purchased it, building the stunning Sainte-Chapelle in 1248 to house the relic. It is now in Notre Dame Cathedral in Paris.
Likewise, the Holy Lance (also the "Spear of Destiny" or "Spear of Longinus," after the traditional name of the Roman soldier who owned it) is said to have been the spear that pierced Jesus' side during the crucifixion (John 19:34). Again there are several rival relics, the most famous being the Holy Lance in the Imperial Treasury in Vienna.
These relics were believed to be a conduit by which Christ's spiritual power could by physically transferred to the believer who saw, venerated or touched the holy relics. To touch such a relic, it was believed, was the closest most people can come to touching God.