On the Via Labicana are several interesting Catacombs. About a mile and a half from the city is that of Peter and Marcellinus, the former a priest and the latter an exorcist of the time of Diocletian, who with other martyrs are said to be buried here. The entrance to the Catacomb is from a church built in the ruins of the ancient structure traditionally called the mausoleum of Helena. This tradition has given its name to the interesting Catacomb of Helena discovered in 1838 in the Vigna del Grande, about a quarter of a mile further along the Via Labicana. It was evidently constructed after the peace of the church. The marble stairway, mosaic pavements, and elegant stucco ornaments betray an imperial magnificence impossible during the age of persecution, and which is found in no other Catacomb. The similarity of style and material to that of the contiguous tomb of Constantia, the sister of Helena, indicates a synchronous construction. The entrance to the Catacomb is by one of those _brevissimæ ecclesiæ_, or oratories for meditation and prayer, which were early erected near most of the cemeteries, now generally in ruins. As shown in the illustration, the descent is by an easy stairway and an inclined plane to a vaulted gallery with mosaic pavement, in which are _arcosolia_ with brick arches. The galleries are of great width, and the _luminari_ will be observed to be cylindrical in shape. One of these, it will be seen, is choked with 191 rubbish. The double entrance indicated is in accordance with the ancient usage, especially in subterranean assemblies, of separating the sexes. The same purpose is effected within the crypt by balustrades, and even by parallel galleries to the same chamber. This Catacomb is remarkable for the number of its _luminari_, _arcosolia_, _cubicula_, and mosaics. A variety of marble, glass, and terra cotta vases have also been found, as well as numerous coins and medals of the Constantinian period. [Illustration: Fig. 29.--Section of Catacomb of Helena.] About three miles from Rome on this road, in the Vigna del Fiscale, is the Catacomb of _i Santi Quatro_, or _Quatuor Coronati_, the Four Crowned Ones, as they are called. They are said to have been Christian sculptors, who, for refusing to exercise their art in the service of idolatry, suffered martyrdom under Diocletian. Iron crowns, set with spikes, were forced upon their heads, and they were then scourged to death with _plumbatæ_. Ten miles from Rome in this same road is the Catacomb of St. Zoticus, also honoured as one of the primitive martyrs.