The ground within, which we call the acropolis, is the flat top of the hill, around which the wall forms approximately three sides of a hexagon (omitting the northern portion which descends, as we have seen, to a lower level). The length of the wall upon the acropolis is about one and a half miles, and the greatest width across from east to west is about three-quarters of a mile. The whole circuit of the defences, including the lower portion, is about three miles and a half; while the greatest length from north to south upon the plan is about one mile and a quarter, of which about half lies on the upper level. The city wall, though built without mortar, was constructed in such a way that it is still traceable continuously around the acropolis, and is preserved in many places to a height of twelve feet or more. It has an average thickness of about fourteen feet, made up of an inner and outer facing each about four feet thick, padded with a core of stone between. The outer face was especially strong, consisting of large stones sometimes as much as five feet in length (but averaging from two feet six inches at the bottom to one foot towards the top), dressed so as to fit cleanly together, with a preference for an approximately rectangular or five-sided form. The masonry was laid in courses as far as practicable with such material, but was liable to be interrupted by a stone larger than usual, or from other cause. Indeed, in some of the inner walls, where the masonry is less massive though similar in character, large stones have been inserted at intervals as a bond and to give general stability. The contour of the wall was further strengthened by buttresses or extra-mural towers, placed at intervals which varied according to the situation, averaging about a hundred feet apart. These do not seem to have been designed from principles of defence, but solely as architectural supports.[479] [Illustration: PLATE LIX BOGHAZ-KEUI: GORGE OF THE BEUYUK KAYANIN DARESI On the left, Beuyuk Kaleh. (_See p. 200._)]