Here and here alone did the early kings leave memorials of their presence in Babylon; and here consequently, we may presume, stood the ancient royal residence.
If, then, all the principal ruins on the east bank of the river, with the exception of the Babil mound and the long lines marking walls or embankments, be accepted as representing the "great palace" or "citadel" of the classical writers we must recognize in the remains west of the ancient course of the river-the oblong square enclosure and the important building at its south-east angle--the second or "smaller palace" of Ctesias, which was joined to the larger one, according to that writer, by a bridge and a tunnel.

This edifice, built or at any rate repaired by Neriglissar, lay directly opposite the more ancient part of the eastern palace, being separated from it by the river, which anciently flowed along the western face of the Kasr and Amran mounds.
The exact position of the bridge cannot be fixed.

With regard to the tunnel, it is extremely unlikely that any such construction was ever made.

The "Father of History" is wholly silent on the subject, while he carefully describes the bridge, a work far less extraordinary.
The tunnel rests on the authority of two writers only--Diodorus and Philostratus--who both wrote after Babylon was completely ruined.

It was probably one of the imaginations of the inventive Ctesias, from whom Diodorus evidently derived all the main points of his description.
Thus far there is no great difficulty in identifying the existing remains with buildings mentioned by ancient authors; but, at the point to which we are now come, the subject grows exceedingly obscure, and it is impossible to offer more than reasonable conjectures upon the true character of the remaining ruins.