The basin of the Caspian has to boast of the largest and most important of the rivers of Russia, and, in fact, of Europe, the Volga. This river was formerly considered as constituting a part of the boundary-line between Europe and Asia; but since the limits of these continents have been removed to the Caucasus and the Caspian, its basin, with those of its tributaries, lie wholly within Europe. From its source to its mouth its length is estimated at near two thousand miles, being about two hundred miles longer than the Danube. The area of its basin has been supposed to include upward of six hundred and thirty-six thousand square miles, or considerable more than twice as much as the basin of the Danube.
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Sears, Robert. An Illustrated Description of the Russian Empire. New York: Robert Sears, 1855