The porphyry columns of the western exedras have a total height of thirty-one feet; the shafts are twenty-two feet and three-quarters long, and the diameter at the bottom is three feet one inch. The capital is four feet high, and the abacus above measures towards the nave four feet nine inches, and towards the aisles four feet eleven inches. In the direction of the thickness of the arch the side of the abacus measures five feet, the variation being due to the circular plan of exedras. The columns of the upper storey, which separate the gynaeceum and the nave, also of verde antique, stand nearer to one another and are smaller than those below. The total height of those in the middle division is twenty-two feet five inches; those in the exedras are twenty-one feet, with a diameter at the bottom of two and a quarter feet. The capitals are three and a half feet high, and the bases, including a six-inch bronze ring, two feet one inch.[262] The parapet is three feet ten inches high, and of white marble.[263] It stands between the columns, and like them is set on a stylobate one foot six inches high, above the lower cornice. It should be noticed how the wide vaulting of the aisles is contrived, so as not to interfere with the view through the arched openings of the lower range of columns. The columns in the interior of the ground-floor aisles are about twenty-four feet seven inches high. These capitals are similar to those already described. Those in the interior of the gynaeceum, with shafts of Proconnesian marble, have capitals of quite another form.[264] They are very similar to others in the church of SS. Sergius and Bacchus; the twin columns in the gynaeceum at the west end of the nave have similar capitals; the columns being verde antique. In these capitals, however, the volutes are not arranged diagonally, but show “cushions” at the side. The capitals in the atrium resembled those of the twin columns; though the cushion was shorter and the top had less projection, and it was crowned with a flat egg and tongue moulding. The capitals and shafts were of white marble. The beautiful square capitals of the eight square white marble pillars in the aisles are shown in Salzenberg’s Plate xvi. The arches of the great order have an elaborate leaf-ornament round them, continuing above the capitals in a horizontal line, resembling in fact an architrave. [In the centre above each capital is a cross, and at the crown of the arch is a four or six-armed cross.] The spandrils are filled with acanthus-ornament, and in the centre of each is a disc of coloured marble-surrounded by a carved circle in the white marble. The ornament of the intrados of the arches consists of five divisions in the width: these are covered with a continuous pattern, seven slabs casing the intrados of the arch. [The five bands are only carved alternately, the centre and lateral ones being plain.] See our Fig. 50.