Bk. IV. Ch. V. TOMBS. 347 the external walls being slight in construction and octagonal in plan.' We must not in this place pursue any further the subject of the transi- tion of style, as we have already trespassed within the pale of Chris- tian architecture and passed beyond the limits of Heathen art. So gradual, however, was the change, and so long in preparation, that it is impossible to draw the line exactly where the separation actually took place between the two. Temple of Mixerta Medica. One important building remains to be mentioned before leaving this part of the subject. It commonly goes by the name of the Temple of Minerva Medica, though this is certainly a misnomer. Recently it has become the fashion to assume that it was the hall of some bath ; no building of that class, however, Avas known to exist in the neighborhood, and it is extremely improbable that any should ])e found outside the Servian Avails in this direction ; moreover, it is Avanting in all the necessary accompaniments of such an establishment. It is here placed Avith the tombs, because its site is one that would justify its being so classed, and its form being just such as Avould be a])plicable to that ]Jurpose and to no other. It is not by any means cer- tain, however, that it is a tomb, though there does not seem to be any more probable supposition. It certainly belongs to the last days of the Roman Empire, if indeed it be not a Christian building, Avhich I am very much inclined to believe it is, for, on comparing it Avith the Baptistery of Constantino and the tomb of Sta. Costanza, it shows a considerable advance in construction on both these buildings, and a greater similarity to San Vitale at Ravenna, and other buildings of Justinian's time, than to anything else now found in Rome. As Avill be seen from the plan and section (Woodcuts Nos. 227 and 228), it has a dome, 80 ft. in diameter, resting on a decagon of singu- larly light and elegant construction. Nine of the compartments con- tain niches which give great room on the floor, as well as great variety and lightness to the general design. Above this is a clerestory of ten Avell-proportioned Avindows, which give light to the building, perhaps not in so effective a manner as the one eye of the Pantheon, though by a far more convenient arrangement, to protect from the elements a ])eople Avho did not possess glass. So far as I know, all the domed buildings erected by the R®mans up to the time of Constantine, and indeed long afterwards, were circular in the interior, though, like the temple built by Diocletian at Spalatro, they Avere sometimes octagonal externally. These two buildings are described furtber on (p. 431) as Christian edifices.
