Of the second completed scheme a terrace of brick rubble was constructed over the entire area, of which the upper level lies at 8 metres above zero. On this terrace stand the foundation walls of the palace, which even now rise as high in parts as 15.5 metres. At about this height the ancient pavement must have been laid. The space between the foundation walls was built up with brick rubble. Thus, in comparison with the Southern Citadel, immense care has been bestowed on the regularity of the foundations. The area lies immediately north of the Arachtu wall, which points to the conclusion that the Principal Citadel was constructed in the bed of the original watercourse, and this explains the unusual form of foundations both here and in the western part of the Southern Citadel, which also overlapped the ancient Arachtu wall. [Illustration: FIG. 98.—Blocks of brickwork in the Principal Citadel. ] In the great courts round which the palace buildings are grouped, as in the Southern Citadel, the filling of brickwork is not arranged in a solid mass but in the form of long blocks about 2 metres in breadth and height. One course of these runs from east to west, the next above from north to south, as is clearly seen in _m_ 12, and again in the south-east corner. The bright yellow bricks in the upper parts are some of the hardest and best of those struck by Nebuchadnezzar; 7– or 3–lined stamps are used almost exclusively. In the narrow, often scarcely measurable joints there is fine white lime mortar as hard as stone, and here and there matting or reeds, which, however, do no damage to the hardness of the brickwork. In the lower parts the bricks are redder and softer and the mortar is grey, less solid, and reddish at the edges. For this reason the brick robbers have here preferred to work underground in search of the lower bricks, which are more easily removed. Thus the high walls have been largely robbed of their supports, and they are now sunk and split, as though they had been flung together by an earthquake (Fig. 98). During the progress of the building the details of the plan were frequently altered. Walls were thrown down and doors were displaced, so that at every 10th or 12th course a new plan was adopted. The royal builder must have insisted very specially and with great energy on his own wishes being carried out, for no architect would of his own free will alter plans so frequently during the course of building. The decorations were still more splendid than those of the southern palace. Remains have been found of large reliefs consisting of a beautiful blue paste, similar to lapis lazuli. The figures were made up of separate pieces, each of which only contained a small part, such as a lock of hair. On the back of these separate pieces there was a prismatic addition, by which they were affixed to some background of which we know nothing. [Illustration: