Is there a bone of saint buried under the altar of a Catholic Church?

From the earliest years of the Church until recently it has been customary to place a first class relic (small piece of the body) of a saint, usually a martyr, in an altar stone that is part of the altar. This is no longer a requirement. This was in remembrance of the early years when Mass was said in the catacombs on the tombs of the martyrs.