Originally, before the interior was narrowed in the way we have explained, there was a much clearer suggestion of a cross plan: barrel vaults at north and south being filled at their ends with large lunettes like the west vault. We suppose that the failure was mainly in the secondary order, and that the window screen and all possible weight was entirely removed and transferred to the great order. Salzenberg was satisfied that there had been great alterations in this part of the building, and Choisy’s view of the window-wall, Plate xxv., entirely confirms his opinion. If it could be shown that the alteration spoken of by Agathias will not bear the interpretation we put on it, there were earlier troubles at this part mentioned by Procopius. The best proof, however, we suggest is found in the design. It has been before pointed out that Choisy and other writers have too hastily assumed that S. Sophia Salonica was built after the great church of Constantinople. That it preceded it enforces the present argument. Grelot (1680) writes that upper galleries remained in the church in these positions, but he based his assertion on the row of seven arched recesses just above the main cornice which he thought were formerly open. It is clear however from an examination of the section that the arches could only have opened to the vault of the first floor gynaeceum. That these small arches did open to the vault of the first floor, seems to be borne out by the fact that above the centre of the secondary order, where its arch is low, a similar piercing is made, through which (or the higher arches on each side) and through the seven arches, a mysterious perspective into the immensity of the dome might have been obtained by those in the gynaeceum (see Figs. 4, 36, 38). Shallow arched recesses merely used decoratively seem to have been little known to early Byzantine art, and arches on the first floor through the great piers are blocked in a similar way. Moreover such openings would explain why the vault between the two orders of columns is so much stilted up into mere darkness. _Atrium._--To explain the present confused arrangement of the exterior, we must remember that from the time of the description of the church by the Silentiary to its description by Gyllius was a thousand years--as long as from the time of Alfred to the present day--and in this time we may well expect alterations and accretions. In Chapter IX. we have shown that the present form of the exonarthex, with its great external piers, was an alteration, made about the time the belfry was added in the ninth century. Before that time the atrium was alike on all four sides--a true _quadriporticus_--one of the most beautiful features of the ancient churches. (See Figs. 3 and 25.)