The Babylon which has now been partially cleared, though in its central portion it reaches back to the First Dynasty and to the period of Hammurabi, is mainly that of the Neo-Babylonian empire, when Nebuchadnezzar II., and Nabonidus, the last native Babylonian king, raised their capital to a condition of magnificence it had not known before. This city survived, with but little change, during the domination of the Achæmenian kings of Persia, and from the time of Herodotus onward Babylon was made famous throughout the ancient world. At that time Ashur and Nineveh, the great capitals of Assyria, had ceased to exist; but Babylon was still in her glory, and descriptions of the city have come down to us in the works of classical writers. To fit this literary tradition to the actual remains of the city has furnished a number of fascinating problems. How, for example, are we to explain the puzzling discrepancy between the present position of the outer walls and the enormous estimate of the city's area given by Herodotus, or even that of Ctesias? For Herodotus himself appears to have visited Babylon; and Ctesias was the physician of Artaxerxes II. Mnemon, who has left a memorial of his presence in a marble building on the Ḳaṣr. Herodotus reckons that the walls of Babylon extended for four hundred and eighty stades, the area they enclosed forming an exact square, a hundred and twenty stades in length each way.[14] In other words, he would have us picture a city more than fifty-three miles in circumference. The estimate of Ctesias is not so large, his side of sixty-five stades giving a circumference of rather over forty miles.[15] Such figures, it has been suggested, are not in themselves impossible, Koldewey, for example, comparing the Great Wall of China which extends for more than fifteen hundred miles, and is thus about twenty-nine times as long as Herodotus's estimate for the wall of Babylon.[16] But the latter was not simply a frontier-fortification. It was the enclosing wall of a city, and a more apposite comparison is that of the walls of Nanking, the largest city-site in China, and the work of an empire even greater than Babylon.[17] The latter measure less than twenty-four miles in circuit, and the comparison does not encourage an acceptance of Herodotus's figures on grounds of general probability. It is true that Oppert accepted them, but he only found this possible by stretching his plan of the city to include the whole area from Babil to Birs-Nimrûd,[18] and by seeing traces of the city and its walls in every sort of intervening mound of whatever period.