Immediately in front of the northern portion of the west front of the peribolos there lies the Arachtu wall of Nabopolassar, of which we saw the commencement in the north at the Southern Citadel. As soon as we began the cross-cut mentioned above, we came on a length of wall in which was an inscribed brick that explained its purpose. Later on in the farther reaches of the wall we found numerous bricks of the same kind _in situ_. The text is identical with that already quoted on page 138 _et seq._ The wall lies lower than the burnt-brick kisu of the peribolos wall at this point. The Arachtu wall, which stands in water, reaches up only to .33 metres below zero with its ruins, while the kisu of the peribolos extends down to 2.24 metres above zero. The upper level of the river banquette lies without any intermediate space in front of the Nebuchadnezzar wall, which is 6 metres thick, and is exactly at zero level. The Nabopolassar wall consists of unstamped 31–centimetre bricks, the facing wall of 33–centimetre bricks, with the Nebuchadnezzar stamp. The smooth front of both walls faces west, the back is left rough as it was built up against the bank behind. Both walls extend as far as the northern corner of the peribolos. From there the Nabopolassar wall runs in a straight line northwards to a distance of about 20 metres from the Southern Citadel, where it breaks off in ruins. Its line runs approximately on the western boundary of the additional building, and must therefore originally have made a curve in order to join at its commencement with the Sargon wall. From the Nebuchadnezzar wall a branch turns off at a very sharp angle at the above-mentioned place, and runs exactly in the direction of the ancient moat wall. Another branch joins on here with a doubly-grooved expansion joint, and runs in the direction of the northern part of the Nabonidus wall. Thus there are parts of four walls close together here, all of which belong to four consecutive changes in direction. At the same place a culvert passes through each of the walls, which must have carried off the surface water that collected to the north of the peribolos. Somewhat farther to the north we came upon two descending stairways in the Nabopolassar wall, which were walled up in a second building period. They are similar to those in the gateways in the Nabonidus wall.