In mountain regions which are also arid, the identity of a district with a stream basin becomes yet more pronounced, because here population must gather about the common water supply, must organize to secure its fair distribution, and cooperate in the construction of irrigation channels to make the distribution as economical and effective as possible.  Thus in Chinese Turkestan, the districts of Yarkand, Kashgar, Aksu and Kut-sha are identical with as many mountain tributaries of the Tarim, whose basin in turn comprises almost the whole of Chinese Turkestan.

[Sidenote:  Enclosed river valleys.]

In all such desert and mountain-rimmed valleys, the central stream attracts to its narrow hem of alluvial soil the majority of the population, determines the course of the main highroad, and is itself often the only route through the encompassing barriers.  Hence the importance attached to the river by the inhabitants, an importance reflected in the fact that the river often gives its name to the whole district.  To the most ancient Greeks Aigiptos meant the river, whose name was later transferred to the whole land; for the narrow arable strip which constituted Egypt was “the gift of the Nile.”  The Aryans, descending into India through the mountains on its northwest border, gave the name of Sindhu, “the flood” or “the ocean,” to the first great river they met.  In the mouth of Persians and Greeks the name was corrupted into Indus, and then applied to the whole country; but it still survives in its original form in the local designation of the Sind province, which comprises the valley of the Indus below the confluence of the five rivers, which again formed and named the original Punjab.  Significantly enough the western political boundary of the Sind extends into the barren foothills of Baluchistan only so far as the affluents of the Indus render the land arable by irrigation; for the Indus performs for the great province of the Sind, by annual inundation and perennial irrigation, the same service that the Nile does for Egypt.

The segregation of such districts, and the concentration of their interests and activities along the central streams have tended to develop in the population an intense but contracted national consciousness, and to lend them a distinctive history.  Their rivers become interwoven with their mythology and religion, are gods to be worshipped or appeased, become goals of pilgrimages, or acquire a peculiar sanctity.  The Nile, Ganges, Jamna, Jordan, Tiber and Po are such sacred streams, while the Rhine figures in German mythology.

[Sidenote:  Rivers as boundaries of races and peoples.]