But its most important provinces were the western ones.

East of Persepolis, the only regions of much value were the valleys of the Indus and the Oxus.

Westward lay Susiana, Babylonia, Assyria, Media, Armenia, Iberia, Cappadocia, Asia Minor, Cyprus, Syria, Palestine, Egypt, the Cyrenaica--all countries of great, or at least considerable, productiveness.

The two richest grain tracts of the ancient world, the best pasture regions, the districts which produced the most valuable horses, the most abundant of known gold-fields, were included within the limits of the Empire, which may be looked upon as self-sufficing, containing within it all that man in those days required, not only for his necessities, but even for his most cherished luxuries.
The productiveness of the Empire was the natural result of its possessing so many and such large rivers.

Six streams of the first class, having courses exceeding a thousand miles in length, helped to fertilize the lands which owned the sway of the Great King.