Cyrus, however, had a motive for his proceedings which will appear in the sequel.  Having wintered on the banks of the Gyndes in a mild climate, where tents would have been quite a sufficient protection to his army, he put his troops in motion at the commencement of spring, crossed the Tigris apparently unopposed, and soon came in sight of the capital.  Here he found the Babylonian army drawn out to meet him under the command of Nabonadius himself, who had resolved to try the chance of a battle.  An engagement ensued, of which we possess no details; our informants simply tell us that the Babylonian monarch was completely defeated, and that, while most of his army sought safety within the walls of the capital, he himself with a small body of troops threw himself into Borsippa, an important town lying at a short distance from Babylon towards the south-west.  It is not easy to see the exact object of this movement.  Perhaps Nabonadius thought that the enemy would thereby be obliged to divide his army, which might then more easily be defeated; perhaps he imagined that by remaining without the walls he might be able to collect such a force among his subjects and allies as would compel the beleaguering army to withdraw.  Or, possibly, he merely followed an instinct of self-preservation, and fearing that the soldiers of Cyrus might enter Babylon with his own, if he fled thither, sought refuge in another city.

It might have been supposed that his absence would have produced anarchy and confusion in the capital; but a step which he had recently taken with the object of giving stability to his throne rendered the preservation of order tolerably easy.  At the earliest possible moment—­probably when he was about fourteen—­he had associated with him in the government his son, Belshazzar, or Bel-shar-uzur, the grandson of the great Nebuchadnezzar.  This step, taken most likely with a view to none but internal dangers, was now found exceedingly convenient for the purposes of the war.  In his father’s absence Belshazzar took the direction of affairs within the city, and met and foiled for a considerable time all the assaults of the Persians.  He was young and inexperienced, but he had the counsels of the queen-mother to guide and support him, as well as those of the various lords and officers of the court.  So well did he manage the defence that after a while Cyrus despaired, and as a last resource ventured on a stratagem in which it was clear that he must either succeed or perish.

Withdrawing the greater part of his army from the vicinity of the city, and leaving behind him only certain corps of observation, Cyrus marched away up the course of the Euphrates for a certain distance, and there proceeded to make a vigorous use of the spade.  His soldiers could now appreciate the value of the experience which they had gained by dispersing the Gyndes, and perceive that the summer and autumn of the preceding year had not been wasted.  They dug a channel or channels from the Euphrates, by means of which a great portion of its water would be drawn off, and hoped in this way to render the natural course of the river fordable.