In the Cathedral dedicated to Sant'Antioco there are Christian catacombs which, in respect of the more famous structures of Rome, have a very special feature: it was not necessary to dig to obtain the gallery branches, but only to resort to rehashing the vast Punic necropolis (VI-IV century B.C.) and clearing the ancient burial chambers from the previous depositions in order to form a continuous series of cavities. Underground cemeteries came into use in the Christian world between the fourth and seventh centuries A.D.

According to current knowledge, the underground graves of Sulky which were reused and linked together are seven, belonging to two nuclei with separate entrances: there are therefore the underground grave A + B + L, the D, E, F and the G one and the ambulatory C (fig. 1). Space A has an apse, with the vault supported by six columns and as many capitals reused from previous Roman buildings. At the centre of this small colonnade, which creates a circle, lies the sarcophagus-altar where it is said that the saint's bones were found in 1615 (fig. 2).

Fig. 1 - Plan of the catacombs of Sant'Antioco and of those of Santa Rosa (from http://basilicasantantiocomartire.blogspot.it/p/catacombe.html).

Fig. 2 - Entrance to the catacombs with the altar-sarcophagus of Sant'Antioco (from http://www.parcogeominerario.eu/images/Catacombe%2001.jpg)

The underground grave A + B + L is the one that has undergone most changes. D instead retains the original characteristics of the Punic system as does underground grave E which has undergone some minor changes, but the state of the chamber is much degraded (fig. 3).

Fig. 3 - Hypothetical reconstruction of underground graves A + B + L, D, E, F, G (from PORRU 1989, table IX).

Chamber E was perhaps used for ritual purposes, given the presence inside of a large painted masonry box in which a considerable amount of glassware was found, both in pieces and complete, reported by Taramelli during the exploration in 1921 (fig. 4).

Fig. 4 - Painted sarcophagus in E chamber (from PORRU 1989, table XXII c)

Underground tomb F underwent an expansion in order to obtain a deeper cell than the existing Punic one. Finally chamber G appears very irregular in comparison with the original Punic system and the gravediggers worked in a more radical way, demolishing the partition between two distinct rooms to open a new cell to increase the capacity of the chamber which houses a special canopy tomb (fig. 5).

Fig. 5 - The canopy tomb in chamber G (from PORRU 1989, table XIII)

Besides these chambers, we must remember those of the so-called catacombs of Santa Rosa (fig. 1), formed by areas H and I, whose Punic setup is virtually intact, as they were not reworked: the only Christian elements are represented by two masonry sarcophagi, both inside chamber H, one of which, located immediately to the left of the entrance, is traditionally believed to be the sarcophagus of Santa Rosa, the mother of Sant'Antioco (fig. 6).

Fig. 6 - Entrance to chamber H of the Catacombs of Santa Rosa with one of the sarcophagi on the left.

The Sulcis catacombs are characterised by the presence of the martyrium (fig. 7), and by a structure divided into seven connected rooms.

Fig. 7 - The Martyrium basilica of Sant’Antioco (photo by Unicity S.p.A.).

Further reuse of Punic subterranean rooms by early Christians may be found in the necropolis of Is Pirixeddus, where a small catacomb containing an arcosolium tomb decorated with Christian symbols and with the idealised portrait of the person for whom it was intended was found (fig. 8).

Fig. 8 - Painted Arcosolium in the necropolis of Is Pirixeddus (from Bartoloni 2007, p. 50, fig. 31).

So, what were catacombs? They were burial sites used extensively by early Christians, which were previously, erroneously, regarded as the places in which they hid in order to flee from persecution.