Apart from this, on the entire length of 1½ kilometres of the city wall, there is no indication of any gateway. A short distance from the southern end there is a small mound with walls of burnt brick laid in asphalt, which may perhaps be the remains of a gateway, but which is not yet excavated. Upon the ruins of the wall and near it there are numerous clay coffins, often as many as 30 between one tower and the next. They are widened with a bulge on one side, and many are anthropoid, and may belong to the Persian or latest Babylonian period. The exploration of the inner city wall cannot be regarded as complete. We will now turn back to the Kasr to study the northern extension, which abuts on the Southern Citadel. XXVI THE PRINCIPAL CITADEL That part of the Kasr that is enclosed on the south by the two mud walls, and on the north by the deep valley in square 7 of the Kasr plan (Fig. 13), we call the Principal Citadel. It was enclosed by a fortification wall, which in the east ran by the side of the Procession Street and in the north turned westward in the great valley just mentioned, where it must have reached the Euphrates of that period. The Principal Citadel in this quarter is, however, only the outcome of a second scheme of Nebuchadnezzar, and the one that was actually carried out. The first scheme, which does not appear to have been carried out, only enclosed one half of the area which was later built upon. Of this we have found the remains of a thick wall in the centre of the Principal Citadel which was intended to form the northern end. It (_k_ 13) ran from west to east, and where it reaches the Procession Street it turned in a southerly direction to join the bastion of the fosse wall at the Ishtar Gate. The wall of burnt brick laid in pure asphalt is 17 metres thick, and is therefore one of the strongest and most massive fortification walls we possess. At the part already excavated there is a doorway which leads through the wall and looks like a long passage. On the north side there are outstanding towers; the extension to the west and eventually to the south we have not yet made out. It is only built to a height of 6.8 metres above zero, and at 4.25 it rests on a foundation banquette.