If anywhere this vitalising had not been completed, it would have been in the more decorative forms; but here we find no mere exercise in applying architectural orders, everything is as real and fresh as in the structure. Having the Corinthian and Ionic capitals before their eyes and without forgetting or rejecting them, the Byzantine builders invented and developed an entirely fresh group of capitals fitted in the most perfect way for arched brick construction. As Mr. Freeman has said (_Hist. Essays_, iii. p. 61) of the new architecture: “The problem was to bring the arch and column into union--in other words to teach the column to support the arch.” This was done by shaping the block of marble which formed the capital so that a simple transition from the square block to the circle of the column was formed. When they were sculptured, and most of them are most elaborately sculptured, the general form is not altered but the carving enriches the surface only. The new “Impost capital” is found throughout the great cistern generally known as that of Philoxenus which is usually referred to the time of Constantine. In their study of the vaulted cisterns of Constantinople Forchheimer and Strzygowski have contributed much that is new to our knowledge of the architecture of the city and show that the evidence is entirely against this theory, which was propounded by Gyllius, whom more recent writers have been content to copy. This cistern, known to the Turks as Bin Bir direk (thousand and one columns), they identify with a great cistern which the _Paschal Chronicle_ says was built by Justinian in 528. We believe with them that the architecture of the cistern agrees entirely with what we might expect as an outcome of the special circumstances in the time of the great building era. “Bin Bir direk exhibits the highest development of the art of cistern building, and it thus in its particular sphere resembles S. Sophia; like it the boldness of its construction was never again equalled by the Byzantines. It would be an explanation of the bold achievement if it might be assumed that Anthemius proved his capability in this subterranean work before he made his supreme effort in S. Sophia. Technical features, however, make it seem probable that the builder was an Alexandrine.” [Illustration: FIG. 50.--Columns of Great Order.] [Illustration: FIG. 51.--Capital now Outside Porch at S. Sophia.] “It is of the widest significance for the history of Byzantine art that here throughout the new ‘impost capital’ is employed in its plainest constructive form. It seems not improbable that the daring builder of the cistern was the first to make use of this form of capital which completely broke with classical tradition and is in such perfect accord with the exigencies of arch-architecture.” This is to go too far; for if the cistern is rightly referred to 528 it is probable, as we shall show, that the impost capital had at that time been for many years in use.