At the time when Herodotus and Ctesias visited Babylon, this wall--which was dismantled by the Persians in order to render revolt more difficult--must have been almost everywhere in a state of ruin, but enough of it remained to attract curious travellers, just as the picturesque fortifications of the Greek emperors are one of the sights of modern Constantinople. The more intelligent among them, such as Herodotus, took note of the measurements given to them as representing the original state of the great work whose ruins lay before their eyes and confirmed the statements of their guides.[64] The quarter then still inhabited was the _Royal City_, the true Babylon, whose great public works have left such formidable traces even to the present day. Naturally no vestige of the tunnel under the Euphrates has been found; we may even be tempted to doubt that it ever existed.[65] But we cannot doubt that the two sections of the town were put in communication one with another by a stone bridge; the evidence on that point is too clear to admit of question.[66] The descriptions of the structure give us a high idea of the engineering skill of the Chaldæans. To build such a bridge and insure its stability was no small undertaking. The river at this point is about 600 feet wide, and from twelve to sixteen deep at its deepest part.[67] We need hardly say that for many centuries there has been no bridge over the Euphrates either in the neighbourhood of Babylon or at any other point in Mesopotamia. As for the quays, Fresnel found some parts in very good preservation in 1853.[68] At the point where this discovery was made the quay was built of very hard and very red bricks, completely covered with bitumen so as to resist the action of the water for as long as possible. The bricks bore the name of Nabounid, who must have continued the work begun by Nebuchadnezzar. The description given by Herodotus of the way in which Babylon was built and the circulation of its inhabitants provided for must also be taken as applying to the Royal City. “The houses are mostly three and four stories high; the streets all run in straight lines, not only those parallel to the river, but also the cross-streets which lead to the waterside. At the river end of these cross-streets are low gates in the fence that skirts the stream, which are, like the great gates in the outer wall, of brass and open on the water.”[69] We may perhaps form some idea of Babylon from the appearance of certain parts of Cairo. Herodotus seems to have been struck by the regularity of the plan, the length of the streets, and the height of the houses. In these particulars it was very different from the low and irregularly built Greek cities of the fifth century B.C. The height of the houses is to be explained partly by the necessity for accommodating a very dense population, partly by the desire for as much shade as possible.[70]