The evidence relating to the city's walls and fortifications has been summarized rather fully, as it has furnished the chief subject of controversy in connexion with the excavations. It should be added that the view suggested above is not shared by Dr. Koldewey, whose objections to the proposed identification of Imgur-Bêl rest on his interpretation of two phrases in a cylinder of Nabopolassar, which was found out of place in _débris_ close to the east wall of the Southern Citadel. In it Nabopolassar records his own restoration of Imgur-Bêl, which he tells us had fallen into decay, and he states that he "founded it in the primæval abyss," adding the words, "I caused Babylon to be enclosed with it towards the four winds."[51] From the reference to the abyss, Dr. Koldewey concludes that it had deep foundations, and must therefore have been constructed of burnt, not crude, brick; while from the second phrase he correctly infers that it must have formed a quadrilateral closed on all sides. But that, as we have seen, is precisely the ground-plan we obtain by including the remains of walls west of the river. And, in view of the well-known tendency to exaggeration in these Neo-Babylonian records, we should surely not credit any single metaphor with the accuracy of a modern architect's specification. If a single section of the wall had been furnished, during restoration, with a burnt-brick substructure, it would have been enough to justify the royal claim. The manner in which the Euphrates was utilized for the defence and water-supply of the citadel has also been illustrated by the excavations. The discovery of Sargon's inscriptions proved that in his day the river flowed along the western face of his quay-wall;[52] while the inscriptions on bricks from the three successive quay-walls of Nabopolassar[53] state, in each case, that he used them to rebuild the wall of a channel he calls the "Arakhtu," using the name in precisely the same way as Sargon refers to the Euphrates. The simplest explanation is that in Nabopolassar's time the Arakhtu was the name for that section of the Euphrates which washed the western side of the citadel, and that its use in any case included the portion of the citadel-moat, or canal, along its northern face, which formed a basin opening directly upon the river.[54] The "Arakhtu" may thus have been a general term, not only for this basin, but for the whole water-front from the north-west corner of the citadel to some point on the left bank to the south of it. It may perhaps have been further extended to include the river frontage of the Tower of Babylon, since it was into the Arakhtu that Sennacherib cast the tower on his destruction of the city. Within this stretch of water, particularly along the northern quays, vessels and _keleks_ would have been moored which arrived down stream with supplies for the palace and the garrison. The Arakhtu, in fact, may well have been the name for the ancient harbour or dock of Babylon.