Nabonadius still held Borsippa, and, if allowed to remain unmolested, might have gradually gathered strength and become once more a formidable foe.

Cyrus, therefore, having first issued his orders that the outer fortifications of Babylon should be dismantled, proceeded to complete his conquest by laying siege to the town where he knew that Nabonadius had taken refuge.
That monarch, however, perceiving that resistance would be vain, did not wait till Borsippa was invested, but on the approach of his enemy surrendered himself.

Cyrus rewarded his submission by kind and liberal treatment.

Not only did he spare his life, but (if we may trust Abydenus) he conferred on him the government of the important province of Carmania.
Thus perished the Babylonian empire.

If we seek the causes of its fall, we shall find them partly in its essential military inferiority to the kingdom that had recently grown up upon its borders, partly in the accidental circumstance that its ruler at the time of the Persian attack was a man of no great capacity.