In arid lands, where the scant and variable streams are useless for navigation, but invaluable for irrigation, a rival interest in the limited water supply leads almost inevitably to conflict, and often to the political union of the peoples holding the upper and lower courses, in order to secure adjustment of their respective claims.  The ancient Salassi of the upper Doria Baltea Valley in the Alps drew off all the water of the stream for washing gold, and thus deprived the agricultural people lower down the valley of the water necessary for irrigation.  The result was frequent wars between the two tribes.[682] The offensive is taken by the downstream people, whose fields and gardens suffer from every extension of tillage or increase of population in the settlements above them.  Occasionally a formal agreement is a temporary expedient.  The River Firenze and other streams watering southern Trans-Caspia have their sources in the mountains of northern Persia; hence the Russians, in the boundary convention with Persia of 1881, stipulated that no new settlement be established along these streams within Persian territory, no extension of land under cultivation beyond the present amount, and no eduction of the water beyond that necessary to irrigate the existing fields.[683] Russia’s designs upon Afghanistan aim not only at access to India, but also at the control of the upper Murghab River, on whose water depends the prosperity of the Pendjeh and Merv oases.[684] In such regions the only logical course is the extension of the political frontier to the watershed, a principle which Russia is applying in western Asia, and which California applied in drawing her eastern boundary to include even Goose Lake.

[Sidenote:  Union of opposite river banks.]

Rivers unite.  Ancient Rome grew up on both banks of the Tiber, and extended her commercial and political supremacy up and down stream.  Both sides of the Rhine were originally occupied by the Gallic tribes, whose villages were in some instances bisected by the river.  Caesar found the Menapii, a Belgian people on the lower Rhine, with their fields, farmhouses and villages on both banks.[685] Then the westward advance of the Teutonic tribes gradually transformed the Rhine into a German river, from the island of Batavia at its mouth up to the great elbow at the foot of the Jura Mountains.[686] To the American Indians even the widest rivers were no barriers.  Christopher Gist, exploring the Ohio in 1751, found a Shawnee village situated on both sides of the river below the mouth of the Scioto, with about a hundred houses on the north bank and forty on the south.[687] The small and unique nation of the Mandan Indians were found by Lewis and Clark near the northern bend of the Missouri in 1804, in two groups of villages on opposite sides of the river.  They had previously in 1772 occupied nine villages lower down the stream, two on the east bank and seven on the west.[688] The Connecticut River settlers of early colonial days laid out all their towns straight across the valley, utilizing the alluvial meadows on both banks for tillage, the terraces for residence sites, and the common river for intercourse.[689]