• Architectural term, originally used to designate the burial-place of a confessor or martyr, gradually came to have a variety of applications: the altar erected over the grave; the underground cubiculum which contained the tomb; the high altar of the basilica erected over the confession; later on in the Middle Ages the basilica itself; and finally the new resting-place to which the remains of a martyr had been transferred
Catholic Encyclopedia. Kevin Knight. 2006.
Catholic encyclopedia.