Crawling first through O, one finds one’s self in a spacious vaulted hall, some 200 feet long, and from 29 to 40 feet wide. The lower portion of the hall is filled with _débris_ and earth, piled unevenly upon the floor, in great mounds and deep hollows, which add indeed to the weirdness of the scene, but, unfortunately, render a complete exploration of the interior impossible. Thirteen buttress-walls, pierced by three arches superposed, run transversely across the hall, from the wall AA to the wall BB, and divide the interior into fourteen compartments, which average nearly 10 feet in breadth, and vary in length from about 27 to 40 feet; the walls AA and BB standing further apart, as they proceed from south-west to north-east. These compartments, excepting the first and last, were divided, as the cavities for fixing joists in the buttresses prove, into three stories of twelve chambers, the superposed arches affording continuous communication between the chambers on the different floors. The chambers on the ground floor, so far as appears, were totally dark, but those on the two upper stories received light and air through the large loophole in the wall BB, with which each of them was provided. The compartment C´ led to the chamber in the second story of the tower N, and at the same time communicated at v with the terrace on which the Palace of Blachernæ stood, and where the Mosque of Aivas Effendi is now erected. The face of the wall AA is pierced by two tiers of loopholes, which are openings in two superposed corridors or galleries constructed in the body of the wall AA. These loopholes occur at irregular distances from the buttress-walls, and some of them are partially closed by the latter, while others are completely so. As the galleries in AA are blocked with earth at various points, they cannot be explored thoroughly. At the north-eastern end, the upper gallery opens on the garden of a Turkish house near the Heraclian Wall. Whether the south-western end communicated with the court of the Palace of Blachernæ cannot be determined. Returning to the vestibule _b_, and crawling next through the opening at _i_, the explorer finds himself in F, a vaulted chamber over 29 feet long, and about 17 feet wide. What the original height of the apartment was cannot be ascertained, the floor being covered with a deep bed of fine dark loam, but the ceiling is still some 23 feet high. Below a line nearly 14 feet from the ceiling, as a sloping ledge at that elevation makes evident, the north-eastern and north-western walls of the apartment are much thicker than above that point. Over the ledge in the north-eastern wall is a loophole. The south-eastern wall is strengthened with two arches; while the ceiling is pierced by a circular hole, which communicates with the room on the higher story of the tower. When first explored by Dr. Paspates, a well nearly 18 feet deep was found sunk in the floor.[521]