For FICTION books that are about and/or feature Christian relics.

NOT for relics associated with the Old Testament (example: Ark of the Covenant)

A general definition of Relic: "In religion, a relic usually consists of the physical remains of a saint or the personal effects of the saint or venerated person preserved for purposes of veneration as a tangible memorial." (Wiki)

These can include:
The Holy Grail
The True Cross
The Holy Nails
The Crown of Thorns
The Shroud of Turin
The Veil of St. Veronica
The Holy Tunic of Christ
The Holy Lance (Spear of Destiny)
Bones, blood, body, clothing and things associated with the many Saints

For another list for the Holy Grail specially, see: https://www.goodreads.com/list/show/1...