If we have placed the edifices from which the English explorers have drawn so many precious monuments in the second line, it is not only because their exploration is incomplete, but also because they do not lend themselves to our purpose quite so readily as that cleared by MM. Botta and Place. At Khorsabad there have never been any buildings but those of Sargon; city and palace were built at a single operation, and those who undertake their study do not run any risk of confusion between the work of different generations. The plan we have discussed so minutely is really that elaborated by the Assyrian architect to whom Sargon committed the direction of the work. We can hardly say the same of the ruins explored by Mr. Layard and his successors. The mounds of Nimroud and Kouyundjik saw one royal dwelling succeed another, and the architects who were employed upon them hardly had their hands free. They had, to a certain extent, to reckon with buildings already in existence. These may sometimes have prevented them from extending their works as far as they wished in one direction or another, or even compelled them now and then to vary the levels of their floors; so that it is not always easy for a modern explorer to know exactly how he stands among the ruins of their creations, or to clearly distinguish the work of one date from that of another.[40] It was at Nimroud that this perplexity was chiefly felt, until the decipherment of the inscriptions came to enable different periods and princes to be easily distinguished. This name of Nimroud, handed down by the ancient traditions collected in Genesis, has been given to a mound which rises about six leagues to the south of Mossoul, on the left bank of the Tigris, and both by its form and elevation attracts the attention of every traveller that descends the stream. The river is now at some distance from the ruins, but as our map shows (Fig. 1), it is easy to trace its ancient bed, which was close to the foot of the mound. The latter is an elongated parallelogram, about 1,300 yards in one direction, and 750 in the other (see Vol. I., Fig. 145). Above its weather-beaten sides, and the flat expanse at their summit, stood, before the excavations began, the apex of the conical mound in which Layard found the lower stories of a staged tower (Fig. 13). Calah seems to have been the first capital of the Assyrian Empire and even to have preserved some considerable importance after the Sargonids had transported the seat of government to Nineveh, and built their most sumptuous buildings in the latter city. Nearly every king of any importance, down to the very last years of the monarchy, left the mark of his hand upon Nimroud.[41]