Some have supposed that besides these works there was further built at the same time a great wall which extended entirely across the tract between the two rivers--a huge barrier a hundred feet high and twenty thick--meant, like the Roman walls in Britain and the great wall of China, to be insurmountable by an unskillful foe; but there is ground for suspecting that this belief is ill-founded, having for its sole basis a misconception of Xenophon's.
Nabonadius appears to have been allowed ample time to carry out to the full his system of defences, and to complete all his preparations.
The precipitancy of Croesus, who plunged into a war with Persia single-handed, asking no aid from his allies, and the promptitude of Cyrus, who allowed him no opportunity of recovering from his first false step, had prevented Nabonadius from coming into actual collision with Persia in the early part of his reign.

The defeat of Croesus in the battle of Pteria, the siege of Sardis, and its capture, followed so rapidly on the first commencement of hostilities, that whatever his wishes may have been, Nabonadius had it not in his power to give any help to his rash ally.

Actual war was thus avoided at this time; and no collision having occurred, Cyrus could defer an attack on the great kingdom of the south until he had consolidated his power in the north and the northeast, which he rightly regarded as of the last importance.
Thus fourteen years intervened between the capture of Sardis by the Persian arms and the commencement of the expedition against Babylon.
When at last it was rumored that the Persian king had quitted Ecbatana (B.C.

539) and commenced his march to the south-west, Nabonadius received the tidings with indifference.

His defences were completed: his city was amply provisioned; if the enemy should defeat him in the open field, he might retire behind his walls, and laugh to scorn all attempts to reduce his capital either by blockade or storm.