It is, in fact, the weakest point in the dome, æsthetically considered, that the same dome cannot be made artistically perfect both within and without. If its height be limited to what looks thoroughly well from within, it is so low in its external aspect as to have little artistic value; while, if raised so high as to be an important external feature, it is only seen by a painful effort from within. This is manifest even in the rotunda, where the dome rises from a circular wall, as in the Pantheon and the Temple of Minerva Medica; but it becomes much more so in a pendentive dome, where the angles are externally encumbered with large masses of masonry. In the earlier Byzantine buildings we accordingly find the dome to have been viewed almost solely as an internal feature, and its exterior very much neglected, and in the case of St. Sophia itself no one would be prepared by its low, heavy, external aspect for the unrivalled glories of its interior. Many of the old architects, in fact, gave up the external form altogether, covering over the dome, as at Parma, etc., by an ordinary sloping roof. The change I have last chronicled,--the interposition of a circular wall between the pendentives and the dome,--though by no means in all cases leading to the result I am referring to, was unquestionably the origin of the treatment of the dome as an important external feature. It was, in fact, the elevation of the rotunda upon the top of the pendentives. Unhappily, however, it had at once the effect of lifting up the dome above the level favourable to its internal effect, while, if erected on four arches only, the weight became so serious as usually to limit its use to domes of very moderate sizes. [Illustration: Fig. 418.] [Illustration: Fig. 419.]