AD CORPUS, BASILICA. - This is the technical term used by archaeologists to denote a basilica that has been built near or above the body of a saint in his honour or to facilitate his liturgical cult.
Since in antiquity this cult was paid only to martyrs and these were ordinarily buried in a cemetery, or had subsequently given rise to a cemetery, the ad corpus basilica is in fact equivalent to a cemetery and suburban basilica erected in honour of a martyr. As such it represents an exception to the rule according to which the ordinary basilica or church was built in urban centres and did not contain the body of any martyr, even if it was sometimes dedicated to him. These were then the only churches normally served and provided with their own and stable clergy; whereas those ad corpus had only a custodian or mansionarius who might be any cleric, and were served only on the feast of the martyr and sometimes on other occasions during the year.
The ad corpus basilica, being built in a cemetery, amid tombs and mausolea, was generally erected on very difficult ground. Hence its forms were almost never regular, and only exceptionally of large proportions; moreover, although the basilican form absolutely predominates, it is often not pure, but serves merely as a plan.
In particular it should be noted that there was a tendency to enlarge the space around the altar to make room for the multitude of the faithful; a circumstance which made the use of a wide transept almost normal. The devotion of the faithful who sought to be buried near the martyr (v. AD SANCTOS) gave rise to many appendages of a cemetery character; indeed the church itself ordinarily became a vast cemetery (burials under the floor, side arcades, sarcophagi in every recess, attached mausolea). Moreover, in order to approach more closely the venerated tomb, when this was situated deep underground, semi-circular crypts with horseshoe-shaped corridors were generally constructed. This usage then spread also to urban churches, especially when they housed bodies or relics of martyrs.
The essential requirement for satisfying the desire to approach the venerated body was that the altar should be placed either above it or very near to II. To this end the ground was often deeply cut away to bring the church to the level of the venerated sepulchre, or even a small church was arranged almost entirely underground (S. Ermete, S. Agnese, SS. Nereo e Achilleo in Rome); sometimes special communications were established between the tomb and the altar; sometimes, when it was impossible to make the centre of the church coincide with the tomb, the altar was placed in an eccentric position, provided only that it remained above the martyr’s tomb. In this way the martyr remained as if buried beneath the altar; he guarded the altar, as it was said. From this began the conception of the altar-tomb which gradually superimposed itself and then even replaced the primitive conception of the altar-table.
For the bibliography V. BASILICA. Antonio Ferrua