The war, however, was not even yet at an end.  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.  Had Nebuchadnezzar himself, or a prince of his mental calibre, been the contemporary of Cyrus, the issue of the contest might have been doubtful.  Babylonia possessed naturally vast powers of resistance—­powers which, had they been made use of to the utmost, might have tired out the patience of the Persians.  That lively, active, but not over-persevering people would scarcely have maintained a siege with the pertinacity of the Babylonians themselves or of the Egyptians.  If the stratagem of Cyrus had failed—­and its success depended wholly on the Babylonians exercising no vigilance—­the capture of the town would have been almost impossible.  Babylon was too large to be blockaded; its walls were too lofty to be scaled, and too massive to be battered down by the means possessed by the ancients.  Mining in the soft alluvial soil would have been dangerous work, especially as the town ditch was deep and supplied with abundant water from the Euphrates.  Cyrus, had he failed in his night attack, would probably have at once raised the siege; and Babylonian independence might perhaps in that case have been maintained down to the time of Alexander.

Even thus, however, the “Empire” would not have been continued.  So soon as it became evident that the Babylonians were no match for the Persians in the field, their authority over the subject nations was at an end.  The Susianians, the tribes of the middle Euphrates, the Syrians, the Phoenicians, the Jews, the Idumseans, the Ammonites and Moabites, would have gravitated to the stronger power, even if the attack of Cyrus on Babylon itself had been repulsed.  For the conquests of Cyrus in Asia Minor, the Oxus region, and Afghanistan, had completely destroyed the balance of power in Western Asia, and given to Persia a preponderance both in men and in resources against which the cleverest and most energetic of Babylonian princes would have struggled in vain.  Persia must in any case have absorbed all the tract between Mount Zagros and the Mediterranean, except Babylonia Proper; and thus the successful defence of Babylon would merely have deprived the Persian Empire of a province.