All study of the church in its condition at that time must be based on the exhaustive plates and text of Salzenberg.[235] M. Texier had in 1834 made some drawings at Constantinople, which are now preserved in the library of the Royal Institute of Architects; and several coincidences seem to point to Salzenberg’s having had the use of Texier’s ground plan. In any case Texier was the first to make correct plans including the upper floor, also the atrium, baptistery, and the circular building at the north-east. As Salzenberg made full use of the unique opportunity afforded by the scaffolding, when the building was given over to the workmen, we have thought it wise to give a condensed paraphrase of his account where it is descriptive of the structure, even at the risk of some repetition. Our remarks in other places where they may overlap are the result of our own observation, from different points of view. The rest of this chapter is an abridgment of Salzenberg’s text and descriptive of his plates, and we add nothing unless in notes or square brackets. _Design._--The exterior walls of the atrium, with several entrances, were built of brick, but the inner sides had marble columns between square brick piers, two columns to one pier. These carried semicircular arches. The atrium walks, as remains showed, were barrel-vaulted, and the vaults were formerly covered with mosaic. The parts for which there was evidence remaining are shown in darker hatching in Salzenberg’s plate vi. The outer wall on the north side, with several arched openings; and traces of the western boundary still existed. The long vestibule in front of the narthex has groined vaulting, and large windows in its west wall; there are some Turkish additions to this part. A door from each lateral cloister, and two others from the open atrium, led into it. On either side of the two doors from the court are strong projecting piers, connected above by a wide arch, forming a porch-like shelter over the doors. These four piers rise above the roof of the vestibule.[236] Double tiers of buttress arches spring from each of these piers to the west wall of the church. A close examination of the wall and piers led to the conviction that they are not contemporary with the church, but were built later, though partly of old material.[237] The upper cornices for instance differ. [Modifications here can be explained by removal of Bell Tower, see p. 194.] The piers were probably erected by Byzantine builders, to strengthen the western vault. Five doors lead to the narthex, the windows of which are above the roof of the outer vestibule. The walls are covered with marble, and the vaulting with mosaic; while the walls and ceiling of the exonarthex, are quite plain. Two other doors enter the narthex at its north and south ends, and nine lead from it into the church; the large central entrance being the Royal Door.