Originally the church was approached at the west through an atrium, an outer narthex and a narthex. The atrium cannot now be traced: the exo-narthex and narthex still remain, but it seems probable that the former is not now as it was originally built. The walls and ceiling of the exo-narthex are quite plain. Five doors give entrance into the much larger narthex, the walls of which are covered with marble, and the ceiling has mosaics which have been but little touched. [Illustration: ORNAMENT ON THE BRAZEN LINTEL ABOVE THE PRINCIPAL DOOR OF S. SOPHIA Translation of Inscription: "The Lord said, 'I am the door of the sheep: by Me if any man enter in, he shall be saved and shall go in and out and find pasture.'"] The Christian must enter the church by the north porch, which leads down a flight of steps into the narthex. He walks forward till he faces the midst of the church, and there over the great central door, the largest of the nine which open eastwards from the narthex into the nave, the mosaic can still be traced, for the paint is almost worn off. It shows our Lord on His throne with the gospel in His hand, open at the words "I am the Light of the World." An Emperor kneels at His feet. It is the Imperial door-way, and by it the sovereign always entered the church. Immediately above the door and below the mosaic, is a brass lintel on which may be clearly read the text of the book represented open upon a throne with a dove spreading its wings above. "The Lord said, I am the door of the sheep: by Me if any man enter in, he shall be saved and shall go in and out and find pasture." A heavy curtain falls over the doorway. It is moved aside and we stand in a space that seems enormous. The eye looks forward to find itself carried upward to the great dome. The great arches on the floor support the smaller arches of the galleries, which extend north, south and west. From these again the eye is carried to the smaller semi-domes, thence to the great semi-domes east and west, and so to the great dome which is the centre of all. The scheme seems at once amazingly intricate and exceedingly simple. There is an infinity of detail, but it is never irrelevant to the main idea, and in an extraordinary manner the feeling of unity is dominant at every point. It is impossible to rest content with any part: the architect compels you to see the part only in its relation to the whole.