13. A dominion so resting on physical force, and gorged with booty wrested from others, with no moral power or national spirit underlying it, could not last long. A more vigorous and warlike power rose by the union of the Persians and Medes under the Persian warrior, Cyrus, who, after a series of conquests farther north and west, in Asia Minor, turned his arms against Babylon. The walls were impregnable, but the river proved a source of weakness. It had been once diverted from its course to pave its bed within the city; the hint was accepted, and, on a night of feasting and carelessness, it was again turned aside to give free entrance to the besiegers, and the Babylonian Empire fell in the very height of its pomp and glory. We find a regular progress in organization, in most institutions, from the first Chaldean to the last Babylonian Empire. In popular religion alone was there an increasing grossness, which reached its limit about this time by the fall of the Chaldean priesthood, purer practices and ideas were circulated by the Jews in their captivity, and the Magian religion was reformed by Zoroaster. 14. The Medo-Persian Empire lasted for 200 years. Those nationalities were both of the Aryan or Indo-European race. They had long been maturing on the highlands bordering the north and east of Chaldea and Assyria, with which their connection was close enough to communicate the general value of the growing organization, but too slight to drag them down to its level. They brought now, to the common stock of progress, the freshness of youth and the healthy habits and pure blood of the mountaineer. They had a higher capacity for organization, by which the experience and progress of the older nations, for more than two thousand years, was prepared to profit. They had already subdued Asia Minor and their vast Empire soon extended from India to the sea that washed the shores of Greece. A complicated civil and military organization consolidated this extensive region more perfectly than before by armies and governors located in each nation and principal city; a system of easy communication was introduced; and the preparation for the higher Greek models of thought, and the severe regularity of Roman institutions went on apace. 15. Babylon fell gradually into decay, being only occasionally the capital of the Persian Empire; the love of the sovereigns of that race for their native highlands leading them to build splendid capitals in the borders of their own country. A reform of great significance occurred about this time in the Persian national religion, which gradually displaced the debasing superstitions and gross idolatry of all the nations of the Empire.