The new form of tomb retained externally the circular form of the Pelasgic sepulchre, though constructive necessities afterwards caused it to become polygonal. Instead however of being solid, or nearly so, the walls were only so thick as was necessary to support the dome, which became the universal form of roof of these buildings.
The sepulchres of Rome have as yet been far too carelessly examined to enable us to trace all the steps by which the transformation took place, but as a general rule it may be stated that the gradual enlargement of the central circular apartment is almost a certain test of the age of a tomb; till at last, before the age of Constantine, they became in fact representations of the Pantheon on a small scale, almost always with a crypt or circular vault below the principal apartment.
226. Section of Sepulchre at San Vito. No scale.
One of the most curious transitional specimens is that found near San Vito, represented in Woodcut No. [226]. Here, as in all the earlier specimens, the principal apartment is the lower, in the square basement. The upper, which has lost its decoration, has the appearance of having been hollowed out of the frustum of a gigantic Doric column, or rather out of a solid tower like the central one of the Tomb of Aruns (Woodcut No. [176]). Shortly after the age of this sepulchre the lower apartment became a mere crypt, and in such examples as those of the sepulchres of the Cornelia and Tossia families we have merely miniature Pantheons somewhat taller in proportion, and with a crypt. This is still more remarkable in a building called the Torre dei Schiavi, which has had a portico attached to one side, and in other respects looks very like a direct imitation of that celebrated temple. It seems certainly, however, to have been built for a tomb.
Another tomb, very similar to that of the Tossia family, is called that of Sta. Helena, the mother of Constantine. If it is not hers, it belongs at any rate to the last days of the Empire, and may be taken as a fair specimen of the tombs of that age and class. It is a vast transition from the tomb of Cæcilia Metella, though, like all the changes introduced by the Romans, it shows the never-failing tendency to transfer all architectural embellishments from the exterior to the interior of every style of building.
227. Section and Elevation of Tomb of Sta. Helena, Rome. No scale.
It consists of a basement about 100 ft. square, containing the crypt. On this stands a circular tower in two storeys. In the lower storey is a circular apartment about 66 ft. in diameter, surrounded by eight niches; in the upper the niches are external, and each is pierced with a window. The dimensions of the tomb are nearly the same as those of Cæcilia Metella, and it thus affords an excellent opportunity of comparing the two extremes of the series, and of contrasting the early Roman with the early Christian tomb.
The typical example of a sepulchre of this age is the tomb or baptistery of Sta. Costanza, the daughter of Constantine (Woodcut No. [423].) In this building the pillars that adorned the exterior of such a mausoleum, for instance, as that of Hadrian, are introduced internally. Externally the building never can have had much ornament. But the breaks between the lower aisle and the central compartment, pierced with the clerestory, must have had a very pleasing effect. In this example there is still shown a certain degree of timidity, which does not afterwards reappear. The columns are coupled and are far more numerous than they need have been, and are united by a fragment of an entablature, as if the architect had been afraid to place his vault directly on the capitals. Notwithstanding these defects, it is a pleasing and singularly instructive example of a completed transformation, and is just what we miss in those secular buildings for which the Christians had no use.