Chaldaea, though it had been now for above half a century an Assyrian fief, and had borne the yoke with scarcely a murmur during that period, could never wholly forget its old glories, or the long resistance which it had made before submitting to its northern neighbor.
The overtures of the Median monarch seem to have been favorably received; and it was agreed that an army from the south should march up the Tigris and threaten Assyria from that quarter, while Cyaxares led his Medes from the east, through the passes of Zagros against the capital.

Rumor soon conveyed the tidings of his enemies' intentions to the Assyrian monarch, who immediately made such a disposition of the forces at his command as seemed best calculated to meet the double danger which threatened him.

Selecting from among his generals the one in whom he placed most confidence--a man named Nabopolassar, most probably an Assyrian--he put him at the head of a portion of his troops, and sent him to Babylon to resist the enemy who was advancing from the sea.

The command of his main army he reserved for himself, intending to undertake in person the defence of his territory against the Medes.

This plan of campaign was not badly conceived; but it was frustrated by an unexpected calamity, Nabopolassar, seeing his sovereign's danger, and calculating astutely that he might gain more by an opportune defection from a falling cause than he could look to receive as the reward of fidelity, resolved to turn traitor and join the enemies of Assyria.
Accordingly he sent an embassy to Cyaxares, with proposals for a close alliance to be cemented by a marriage.