Any altar, by definition, is a structure on which sacrifice is offered. Sacrosanctum Concilium repeatedly speaks of the Mass as a sacrifice, noting that at the Last Supper, Christ instituted “the Eucharistic sacrifice of His Body and Blood” in order to “perpetuate the sacrifice of the cross through the centuries” (47). The very same sacrifice that Christ offered to the Father on the cross was instituted “in the form of a sacrificial banquet.”¹² The Christian altar, then, is fundamentally different from other altars through history because it is not simply a dedicated table upon which gifts are offered to a god. It is Christ present among his people, who then receive the sacrifice that he offers “on” his very person. This sacrificial quality is further expressed by the inclusion of relics under the altar. Traditional explanations claim that the liturgy was celebrated upon the tombs of martyrs in the catacombs of early Christian Rome. Today’s liturgical instructions, however, give primacy to the altar as the object which renders honor to the burial place of martyrs, and so the presence of relics indicates not the sacrifice of the martyrs alone, but more precisely their share in the sacrifice of Christ. The Order of the Dedication of an Altar notes that it is fitting for saints’ relics to be placed under altars so that “the triumphant victims come to their rest in the place where Christ is victim” (5).

In designing a new altar, its sacrificial character should be expressed. One of the most effective ways to accomplish this is to make the “Mensa” out of stone of significant thickness, perhaps three inches or more. A colorful stone given a high polish will indicate a glorified altar, one that has taken on gem-like qualities that signify heavenly conditions (Rv 21:19). Relics are no longer placed in the “Mensa” itself as they once were, where a piece was removed from the top slab to insert the relics. According to today’s liturgical instructions, relics are placed underneath rather than within the altar slab itself. This preserves the integrity of the “Mensa” as an image of Christ, and reinforces the place of relics under, and not in, the altar. In this way, the sign value of the altar as an image of the martyrs participating in Christ’s own sacrifice becomes clear, helping the signs lead to revelation of the mysteries.