epose.

As examples of design which, while meeting the structural necessities
and acknowledging the control of space and general conditions, as the
form of the slabs upon which they are sculptured, yet expresses
independent movement, the figures of the octagonal tower of the winds at
Athens are interesting (see illustration, p. 115[f068]).

Quite a different feeling, corresponding to differences in conception
and spirit in design, comes in with the Roman round _arch_ its allied
forms of _spandril_ and _vault_, _lunette_ and _medallion_, presenting
new spaces for the surface designer, and new suggestions of ornamental
line (see illustration, p. 117[f069]). It is noticeable how, with the
round-arched architecture under Roman, Byzantine (see illustration, p.
118[f070]), and Renaissance forms, the scroll form of ornament
developed, the reason being, I think, that it gave the necessary element
of recurring line, whether used in the horizontal frieze in
association with round arches, or in spandrils of vaults and arcades,
and on marble mosaic pavements.

[Illustration (f069): Sketch of Part of the Arch of Constantine to Show
Spaces for Decorative Sculpture in Roman Architecture.]

[Illustration (f070): Byzantine (Mosaic) Treatment of Architectural
Structural Features: Apse, S. Vitale Ravenna.]

[Value of the Recurring Line]

The development of Gothic architecture, with its new constructive
features and the greater variety of geometric spaces, forms, and
interstices which, as a consequence, were available for the designer of
associated ornament, whether carved work, mosaic, stained glass, or
painting, naturally led to a corresponding variety in invention and
decorative adaptation; and we may trace the same principle at work in
other forms--I mean the principle of corresponding, counterbalancing,
and recurring line--Gothic ornament being indeed generally an essential
part of the structure, and architectural features being constantly
repeated and utilized for their ornamental value, as in the case of
canopies and tabernacle work.

We see, for instance, in the Decorated period the acute gable moulding
over the arched recess, niche, doorway, or tomb, lightened and vivified
by a floriated finial springing into vigorous curves from a vertical
stem, forming an emphatic ogee outline which re-echoes the ogee line of
the arch below, and is taken up in variations by the crockets carved