“for in midway were vast rivers, fearful waters, and first the ocean,”[355] into which all the Indian rivers discharge themselves; then Ariana, the Persian and Arabian Gulfs, all Arabia and Troglodytica. The above is what has been said on the subject of winds and rains, the rising of rivers, and the inundation of plains. 26. We must describe these rivers in detail, with the particulars, which are useful for the purposes of geography, and which have been handed down to us by historians. Besides this, rivers, being a kind of physical boundaries of the size and figures of countries, are of the greatest use in every part of the present work. But the Nile and the rivers in India have a superiority above the rest, because the country could not be inhabited without them. By means of the rivers it is open to navigation and capable of cultivation, when otherwise it would not be accessible, nor could it be occupied by inhabitants. We shall speak of the rivers deserving notice, which flow into the Indus, and of the countries which they traverse; with regard to the rest we know some particulars, but are ignorant of more. Alexander, who discovered the greatest portion of this country, first of all resolved it to be more expedient to pursue and destroy those who had treacherously killed Darius, and were meditating the revolt of Bactriana. He approached India therefore through Ariana, which he left on the right hand, and crossed the Paropamisus to the northern parts, and to Bactriana.[356] Having conquered all the country subject to the Persians, and many other places besides, he then entertained the desire of possessing India, of which he had received many, although indistinct, accounts. He therefore returned, crossing over the same mountains by other and shorter roads, having India on the left hand; he then immediately turned towards it, and towards its western boundaries and the rivers Cophes and Choaspes.[357] The latter river empties itself into the Cophes,[358] near Plemyrium, after passing by another city Gorys, in its course through Bandobene and Gandaritis.[359]