A. Temple of Jupiter.
There are other domes not differing materially from those already described, but which it would extend my lecture unduly to dwell upon. One called the Torre dei Schiavi, in the Via Prænestina, is rather like the Pantheon on a very small scale, though lighted by round clerestory windows instead of a central eye. The Temples of Vesta, both at Rome and at Tivoli, consist of circular walls surrounded externally by a peristyle. The cell of each is supposed to have been covered by a dome, though roofed over. A parallel case, but in a more complex form, exists in what is called the Temple of Jupiter in Diocletian’s Palace at Spalatro ([Fig. 403]). In this case the exterior of the cell, with its peristyle, is octagonal, but the interior, with the dome, round. The latter has a complicated construction of fan-shaped arches throughout, scarcely any part being constructed of horizontal curves. Next, perhaps, in date, yet at once displaying similarity of idea with a significant change in the carrying out, is the tomb of St. Constantia, the daughter of Constantine ([Fig. 404]).
Fig. 404.—Tomb of St. Constantia, Rome. (From Fergusson.)
A Christian church, in its early form, has been familiarly described as the pagan temple turned inside out. To convert the ideal temple into the ideal church, the wall and the colonnade must change places. So completely is this the case that some of the earlier commentators on Vitruvius were completely puzzled between the wall of the temple and the peristyle. They assumed that the latter must be within the wall, as in their own churches, and based their remarks on this supposition.
The comparison between these almost contemporary works, the Temple of Jupiter in Diocletian’s Palace at Spalatro, and the tomb of St. Constantia at Rome, exactly illustrates this change. In the one the solid wall forms the circle and carries the dome, and the colonnade is external (See Fig. 403), in the other the colonnade forms the inner circle and carries the dome, while the wall becomes external, an aisle taking the place of the peristyle (See Fig. 404). The colonnade is doubled to support the massive clerestory whence the dome springs, and the whole assumes the type of one form of Christian church, which henceforth became of frequent occurrence. The dome, in this instance, ceases to be an external feature, being covered over by a conical roof. I may add that the peristyle is repeated in the old manner as an additional feature beyond the wall of the aisle. The baptistery at Nocera is similar in distribution to the tomb of St. Constantia, and may be of similar date. It is ruder, however, and loses much beauty by the omission of the clerestory, and the admission of light through the haunches of the dome. Among the innumerable remains of domes of the older type, I will only mention one more, before proceeding to the second branch of my subject, to which it, in fact, properly belongs. That to which I allude is the baptistery at Ravenna, erected, as it is supposed, about the year 450 ([Fig. 405]).
This is a very charming building, octagonal in form, yet covered over by a hemispherical dome. Though having no surrounding aisle, the design of its sides seems derived from the aisle and clerestory: indeed, it has a clerestory, though the arcade below is rather rudimentary than real. The dome, like that last alluded to, is covered externally by a sloping roof.
The special feature, however, in this dome is that it rests upon an octagonal wall, or rather upon eight arches.