|St. Thomas Chapel in St. Peter’s Basilica
is so named b/c of the altar piece rendition of
St. Thomas’ famous inspection of Jesus’ wounds.
The relics below the altar are of St. Boniface,
so it is also called St. Boniface Chapel.
Dedication of a Church or Altar (DCA) IV, 5. All the dignity of the altar rests on its being the Lord’s table. Thus the martyr’s body does not bring honor to the altar; rather the altar does honor to the martyr’s tomb. For it is altogether proper to erect altars over the burial place of martyrs and other saints or to deposit their relics beneath altars as a mark of respect and as a symbol of the truth that the sacrifice of the members has its source in the sacrifice of the Head. Thus ‘the triumphant victims come to their rest in the place where Christ is victim: he, however, who suffered for all is on the altar; they who have been redeemed by his sufferings are beneath the altar.’ This arrangement would seem to recall in a certain manner the spiritual vision of the Apostle John in the Book of Revelation: ‘I saw underneath the altar the souls of all the people who have been killed on account of the word of God, for witnessing to it.’ His meaning is that although all the saints are rightly called Christ’s witnesses, the witness of blood has a special significance that only the relics of the martyrs beneath the altar express in its entirety.
Revelation 6:9: “I saw underneath the altar the souls of all people who had been killed on account of the word of God, for witnessing to it.”
Canon Law 1237 §2: The ancient tradition of placing relics of martyrs or other saints under a fixed altar is to be preserved, according to the norms given in the liturgical books.
GIRM 302: The practice of placing relics of Saints, even those not Martyrs, under the altar to be dedicated is fittingly retained. Care should be taken, however, to ensure the authenticity of such relics.
DCA II, 5. The tradition in the Roman liturgy of placing relics of martyrs or other saints beneath the altar should be preserved, if possible. But the following should be noted:
a) Such relics should be of a size sufficient for them to be recognized as parts of human bodies. Hence excessively small relics of one or more saints must not be placed beneath the altar.
b) The greatest care must be taken to determine whether the relics in question are authentic. It is better for an altar to be dedicated without relics than to have relics of doubtful authenticity placed beneath it.
c) A reliquary must not be placed upon the altar or set into the table of the altar; it must be placed beneath the table of the altar, as the design of the altar permits.
DCA II, 14. When relics of a martyr are not available, relics of another saint may be deposited in the altar.
DCA VI, 3. [I]t is not permissible to place the relics of saints in the base of a movable altar.
Canon 1235: An altar . . . is called fixed if it is so constructed that it adheres to the floor and thus cannot be moved; it is called moveable if it can be removed.