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.  These were the Nile, the Indus, the Euphrates, the Jaxartes, the Oxus, and the Tigris.  Two of the six have been already described in these volumes, and therefore will not need to detain us here; but a few words must be said with respect to each of the remaining four, if our sketch of the geography of the Empire is to make any approach to completeness.

The Nile was only in the latter part of its course a Persian stream.  Flowing, as we now know that it does, from within a short distance of the equator, it had accomplished more than three fourths of its course before it entered a Persian province.  It ran, however, through Persian territory a distance of about six hundred miles, and conferred on the tract through which it passed immeasurable benefits.  The Greeks sometimes maintained that “Egypt was the gift of the river;” and, though this was very far from being a correct statement in the sense intended, there is a meaning of the words in which we may accept them as expressing a fact.  Egypt is only what she is through her river.  The Nile gives her all that makes her valuable.  This broad, ample, and unfailing stream not only by its annual inundation enriches the soil and prepares it for tillage in a manner that renders only the lightest further labor necessary, but serves as a reservoir from which inexhaustible supplies of the precious fluid can be obtained throughout the whole of the year.  The water, which rises towards the end of June, begins to subside early in October, and for half the year—­from December till June—­Egypt is only cultivable through irrigation.  She produces, however, during this period, excellent crops—­even at the present day, when there are few canals—­from the facility with which water is obtained, by means of a very simple engine, out of the channel of the Nile.  This unfailing supply enabled the cultivator to obtain a second, a third, and even sometimes a fourth crop from the same land within the space of a year.

The course of the Nile from Elephantine, where it entered Egypt, to Cercasorus, near Heliopolis, where it bifurcated, was in general north, with, however, a certain tendency westward.  It entered Egypt nearly in long. 33 deg., and at Neapolis (more than two degrees further north) it was still within 15 deg. of the same meridian; then, however, it took a westerly bend, crossed the 32nd and 31st meridians, and in lat. 28 deg. 23 reached west as far as long. 30 deg. 43’.  After this it returned a little eastward, recrossed the 31st meridian, and having reached long. 31 deg. 22’ near Aphroditopolis (lat.29 deg. 25), it proceeded almost due north to Cercasorus in lat. 30 deg. 7’.  The course of the river up to this point was, from its entry