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.

We have, on the contrary, followed the wall that turns to the east up to the end (Fig. 107). It has a length of about 250 metres, guarded by towers placed closely together, and a door in each mesopyrgion. It represents therefore a site admirably adapted for sorties. The gateway embrasures lie exclusively on the north. At the east the wall turns to the south and joins with one leading from the Procession Street that has not yet been examined in detail. All these eastern walls have been destroyed from the point where they were cut through by the Persian advanced wall down to a great depth, so that it is only with difficulty that a few brick courses could be found above water-level. Above the ruins there lies silt which was evidently formed by water passing over it at some time. On this and immediately below the present level there are remains of later houses either of mud brick or of burnt brick. A little above the ruins, in the line of the northern wall, there was an anthropoid clay coffin (see Fig. 200), the face represented with an Egyptian beard. I believe that the Euphrates, as in Persian times it worked its channel eastwards, thus placing the Kasr on the right bank, first ruined these eastern walls and then formed a muddy peninsula with their ruins, while the actual river flowed still farther east. This is, however, not yet proved.

The position of the double walls that flanked the Procession Street is described in the inscription on a great cylinder that we found on the eastern slope of the Amran hill. It had been used there for some technical purpose, and is much worn. The part that refers to our site runs thus: “At that time I bethought myself to strengthen the stronghold of Babylon. 360 ells of the land the sides (or of the sides) of Nimitti-Bel, the šalḫû of Babylon, I built as a protection from the banks of the Euphrates to the left threshold of the Ištar Gate two mighty walls of asphalt and burnt brick for a dûru like a mountain. Between them I erected a terrace of burnt brick, and upon it a great castle (?) as a dwelling-place of my kingdom. Of asphalt and burnt brick I built high, joined (it) with the palace, which (lay) within the city, and caused the dwelling of my lordship to be glorious. Besides, from the right threshold of the Ištar Gate to the lower turru of Nimitti-Bel in the east 360 ells broadside, (measured) from Nimitti-Bel, for protection, a mighty dûru of asphalt and burnt brick I built mountain high. The stronghold I strengthened with skill. The city of Babylon I protected” (trans. by Weissbach).

As we have seen, the Ishtar Gate had a central door and two side ones. These last are evidently intended for the left- and right-hand thresholds of the Ishtar Gate. The distance from the wall at the threshold to the north side of the bastion on the eastern wall is 192 metres, and on the western wall 196 metres. This gives as measure for Nebuchadnezzar’s ells .533 or .544 metres. These measurements must, however, be taken again more accurately on the completion of the excavations. The length of 490 ells, which is quoted for the same area in the great Steinplatten inscription, includes the northern extension of the wall, to which we shall soon turn.