The stairway communicated, moreover, with the tower N, through narrow vaulted passages that pierce the north-eastern wall of the tower at three points; first, at the original level of the vestibule _b_, and then at the level of the two tiers of loopholes. These passages are choked with earth, but by the partial excavation of the lowest one of them access was obtained to the small chamber D. It had no windows, but a round aperture in the ceiling connected it with some unexplored part of the tower. From this survey of the buildings before us some satisfactory inferences may certainly be drawn regarding their history and character; although several points must remain obscure until the removal of the earth accumulated within the ruins renders a complete exploration possible. In the first place, the character of these walls and towers can be understood only in the light of the fact that whatever other function belonged to them, they were intended to support the terraced hill on which the Palace of Blachernæ, to their rear, was constructed. The unusual height and thickness of the walls, the extent to which buttresses are here employed, were not demanded by purely military considerations. Such features are explicable only upon the view that the fortifications of the city at this point served also as a retaining wall, whereby the Imperial residence could be built upon an elevation beyond the reach of escalade, and where it would command a wide prospect of the city and surrounding country. In fact, the buildings before us resemble the immense substructures raised on the Palatine hill by Septimius Severus and Caracalla to support the platform on which the Ædes Severianæ were erected.[522] [Illustration: “The Tower of Anemas” and “The Tower of Isaac Angelus” (From The South-West).] In the next place, there are at several points in these buildings so many alterations; there is so much undoing of work done, either rendering it useless or diverting it from its original purpose, that these various constructions cannot be treated as parts of an edifice built on a single systematic plan, but as an agglomeration of different erections, put up at various periods to serve new requirements arising from time to time. For instance, the loopholes in the wall AA have no symmetrical relation to the buttress-walls that divide the compartments C; some of them, as already stated, are partially closed by the buttresses; others are entirely so, their existence being discoverable only from the interior of the galleries in the body of that wall. It is hard to believe that such inconsistent arrangements can be the work of one mind and hand.