e 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