346 ROMAN AECHITECTUllE. Part I. On this stands a circular tower in two stories. In the lower story is a circular apartment about 66 ft. in diameter, surrounded by eiglit niches ; in the upper the niclies are external, and each is pierced with a window. The dimensions of the tomb are nearly the same as those of Caecilia Metella, and it thus affords an excellent opportunity of com- paring the two extremes of the series, and of contrasting the early Roman with the early Christian tomb. The typical example of a sepulchre of tliis ^ge is the tomb or bapti- tery of Sta. Costanza, the daughter of Constantine (Woodcut No. 295). In this building the pillars that adorned the exterior of such a mauso- leum, for instance, as that of Hadrian, are introduced internally. Ex- ternally the buildinsTj never can haye had much ornament. But the 226. Section and Elevation of Tomb of Sta. Helena, Home. No scale. breaks between the lower aisle and the central compartment, pierced with the clerestory, must haye had a yery 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. ISTotwithstanding these defects, it is a pleasing and singularly instructive example of a completed transformation, and is just wliat we miss in those secular buildings for which the Chris- tians had no use. Another building, m hich is now known as the Lateran Baptistery (Woodcut No 294), was also undoubtedly a place of sepulture. Its erection is generally ascribed to Constantine, and it is said was in- tended by him to be the ])lace of his own sejuilture. Whether this is correct or not, it certainly belongs to Ids age, and exhibits all the characteristics of the architecture of his time. Here the central apart- ment, never having been designed to support a do)ne, is of a far lighter construction, an upper order of ])illars being placed on the lower, with merely a slight architrave and frieze running between the two orders,
