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.