_The Interior._--The natural division, in height, of an early church, whether basilican or domical, was into three stories--the ground level, the gallery level, and the clearstory or vault level. In the West these structural divisions were developed into the triple composition of nave-arcade, triforium, and clearstory. In the East, in conjunction with the dome, these divisions survive in many examples of the later period. Still, Byzantine architecture was more concerned with spaces than with lines. Large surfaces for marble, painting, or mosaic were of prime importance, and with the disappearance of the gallery the string-course marking the level of the gallery also tended to disappear. In churches with galleries, like S. Theodosia (p. 170) and S. Mary Diaconissa (p. 185), the string-courses fulfil their function, the first marking the gallery level, the second the springing of the vault. In SS. Peter and Mark (p. 193), which has no gallery, there is only one string-course, corresponding in level to the original gallery string-course; accordingly the main arches are highly stilted above it. The absence of the second string-course is a faulty development, for a string-course at the vault level would be a functional member, whereas at the gallery level it is meaningless. In the Panachrantos (p. 130), as well as in other churches without a gallery, the gallery string-course is omitted by a more logical development, and the string-course at the springing of the vault is retained. Openings which do not cut into the vault are then frankly arched, without impost moulding of any kind. Simple vaulted halls, narthexes, and passages have usually a string-course at the vaulting level, broken round shallow pilasters as at the Chora, S. Theodosia, and the Myrelaion. Sometimes the string-courses or the pilasters or both are omitted, and their places are respectively taken by horizontal and vertical bands. Decorative pilasters flush with the wall are employed in the marble incrustation of S. Sophia.