Scholarly Reflections
Mazza, Enrico. "Chapter Thirteen: The Eucharist and the Relics of the Saints." The Celebration of the Eucharist: The Origin of the Rite and the Development of Its Interpretation. Collegeville, MN: The Liturgical Press/Pueblo, 1999, 225-236.
Mazza suggests that the custom of incorporating relics into the altar at church arose from the fact that altars were early erected over tombs of martyrs (Mazza 1999, 225). The consecration of an altar and the case of a relic thus became a very important element of local piety. Mazza looks for a relationship between this presence of a relic in the altar and the sacrament of the Eucharist (Mazza 1999, 226).
In Ordo XLII, probably dating to the eighth century, there are instructions for placement of relics and consecration of an altar (Mazza 1999, 226-227). The consecrated Eucharist is placed in the same box with other relics to be placed in the chamber of the altar (Mazza 1999, 227). There was a process of chrismation, as well as use of holy water in the process of sealing the container. Through the 12th century, there was gradual development of the rites. The practice of placing consecrated eucharistic elements in the box with relics remained the same (Mazza 1999, 229), though it was omitted from some rubrics.
Mazza briefly refers to rubrics from the early 13th century which instruct that if the blood of Christ stains a corporal, that part is cut out and retained as a relic (Mazza 1999, 231). This instruction connects the practice of the eucharistic celebration with that of honoring relics. Mazza notesa hypothesis that the omission of an instruction about placing the eucharistic elements in a box for preservation could be related to the idea that the sacrament is intended for eating, therefore should not be reserved (Mazza 1999, 232). The practice tended to remain in some settings, but not all (Mazza 1999, 233-234).