The court which stands before the Turkish portico in front of the west side of the building represents the old atrium of the church, and to the rear of the portico is still found the ancient narthex. At the south end of the narthex is a stone staircase leading to the gallery. The arch at the foot of the staircase is built of fragments from the old ciborium or eikonostasis of the church. The great height (0.24 metre or 9 inches) of the steps is found, according to Mr. Antoniadi, also in S. Sophia. The exterior walls, which are mostly in brick and rubble masonry, exhibit poor workmanship, and have undergone considerable repair, especially on the east. On the south there are two thicknesses of walling. The outer thickness has arched recesses at intervals along its length, corresponding to openings in the inner thickness, and thus while buttressing the latter also enlarges slightly the area of the church. The length of the rectangular enclosure from west to east is 101 feet, with an average breadth of 772-1/2 feet from north to south, excluding the recesses in the latter direction. All the windows of the church have been altered by Turkish hands, and are rectangular instead of showing semicircular heads. The passage intervening between the rectangular enclosure and the octagon is divided into two stories, thus providing the church with an ambulatory below and a gallery above. The domed octagon which forms the core of the building stands at a distance of some 18-1/2 feet from the rectangle within which it is placed. It measures 53-1/2 feet by 50-1/2 feet. The eight piers at its angles rise to a height of 33-1/2 feet from the floor to the springing of the dome arches. The archways thus formed, except the bema arch, are filled in with two pairs of columns in two stories set on the outer plane of the piers. The lower colonnade is surmounted, after the classic fashion, by a horizontal entablature profusely carved while the upper columns are bound by arches, thus making seven sides of the octagon a beautiful open screen of fourteen columns and as many triple arcades, resplendent with marbles of various hues and rich with carved work. The mass of the piers is relieved by their polygonal form, a fluted cymatium along their summit, and a repeating design of a flower between two broad leaves below the entablature. Though the flower points upwards it has been mistaken for a cluster of grapes.[108] At the four diagonal points the sides of the octagon are semicircular, forming exhedrae, an arrangement which gives variety to the lines of the figure, widens the central area, secures more frontage for the gallery, and helps to buttress the dome. The same feature appears in S. Sophia, whereas in San Vitale all the sides of the octagon, excepting the eastern side, are semicircular. The extension of the interior area of a building (square or octagonal) by means of niches at the angles or in the sides, or both