The Principal Citadel, which adjoins the Arachtu wall on the south, was protected on the east and north by two strong walls, while the western front probably lay open until Nabonidus built his Euphrates wall here. The southern portion of the 7–metres-thick west wall was placed on the old wall of Nebuchadnezzar’s first projected building, which we lighted on in the centre of the Principal Citadel. In it the main entrance to the palace undoubtedly lay, but the wall is not yet completely excavated. Small mud houses backed against the wall and were placed on the upper Nebuchadnezzar pavement, but they were buried below the later pavement that laid the Street horizontal. On the other side of the Procession Street there ran a parallel wall also 7 metres thick. The part that connects it with the Ishtar Gate corresponds with the cross wall on the other side, and like it has shallow foundations. Later a strengthening piece was added to it. It contains two doors close to each other, and a third door lies at a short distance from the northern end. The footing of the wall at the east was concealed by a bank of earth piled up against it, which with its walk on the top reached almost to the height of the Procession Street. At the edge of this walk there is an additional slender wall which may have been built in Persian times, and which appears to have surrounded the whole of the northern Kasr, and to have cut through several of the older walls that stretched eastwards. At the north both walls end in a powerful bastion. These marked the corners at which one turned westward, the other eastward from the Procession Street at an obtuse angle. Transversely across the Procession Street between the bastions there are two mud walls, each with a door in the centre, forming a gateway court, which in conjunction with the bastions bore the appearance of an actual fortified gateway. This gateway was destroyed when the whole length of the Street was laid horizontal with the latest pavement of broken brick. The wall that turned westward protected the palace of the Principal Citadel on the north. Not far from the corner there is a gateway (Fig. 106), which was roofed over at the very moderate height of 1.5 metres with beams of palm wood. Bricks placed upright formed the cavities for inserting the beams, and in them the print of the wood in the asphalt can still be seen; in the middle of the pavement, which is strongly laid in asphalt, a well-shaft led down to the small conduit. This roofed-in space appears to have been only a sort of underground chamber that gave access to the well-shaft; the actual door must have been higher at about the level of the palace. In the outside angle near the bastion Neriglissar constructed a quadrangular well-shaft with his stamped bricks. We have not yet followed up the wall to its western end. [Illustration: FIG. 106.—Doorway with drain, in the north wall of the Principal Citadel. ] [Illustration: