The inscriptions chiselled on the burnt brick (Fig. 90) state that “Nabopolassar, etc., surrounded the Dûr of Babylon with a wall of burnt brick for protection.” Of this we have found only four examples, and they are all in the walls to the north of the Southern Citadel. The beginning of the oldest Nabopolassar wall rests on the round tower of the Sargon wall. Its bricks, which are laid in pure asphalt, are very irregular in size. Their length varies between 30, 31, 32, 33, and 34 centimetres; the last have the chiselled inscriptions. The wall outside has a decided batter and inside is markedly stepped. It reaches only to 20 centimetres below zero, and on it was placed, at the part that runs from north to south, a wall of brick rubble. [Illustration: FIG. 90.—Chiselled brick of Nabopolassar’s Arachtu wall. ] At the rounded-off corner a wall, of which a small portion only now remains, stretches out to the west, and belongs to a second building period (Fig. 91). Immediately in front lies the building of the third period, which towards the east only extends a very short way beyond the corner, but of which the north to south portion adds to the earliest building a strip of land about 16 metres broad. It rises higher, and is as much as one metre above zero; in the west it is formed of broken brick, in the north of crude brick. This wall passes under the two mud walls, and within the Southern Citadel it breaks off with a set-back. This latter must certainly have formed part of an outlet of which the corresponding half must have been destroyed by the building of the Southern Citadel. In this place a bonding of the wall front is employed, which rarely occurs elsewhere. It is formed throughout of one whole brick with a half one behind it, followed by a half brick with a whole one behind it. In the course above there is the same arrangement shifted by a half brick placed sideways. This same method of bonding occurs with Nebuchadnezzar’s bricks at the stairway which leads up to the north-east corner of the Kasr. [Illustration: FIG. 91.—View of north-west corner of the Southern Citadel. ] It is now evident that the older moat wall is also no other than an Arachtu wall, which for the greater part of its northern length lay in front of its predecessor, with no intervening space, while its western portion added once more a strip of land to the old enclosure. XXIII THE WESTERN OUTWORKS