Caspian Sea, an inland sea or great salt lake, the largest in the world, on the boundary between Europe and Asia, extending from 36° 40' to 47° 20' N. lat., and 46° 50' to 55° 10' E. long. Its length from north to south is 680 miles, and its breadth varies between 130 and 270 miles. Its total area is estimated at 170,000 sq. m. The coast-line is irregular, and on the east side especially there are several bays and indentations of coast, the principal being those of Mertviy Kultuk (with the bay Kaidak), Kenderli (separated from the above by the peninsula of Manghishlak), Karabngas, and Balkan. From the west, the naphtha-impregnated peninsula of Apsheron stretches into the Caspian opposite the Balkan Gulf; Mount Caucasus also rises on its west side. On the south rises the lofty range of the Elburz Mountains, between which, however, and the coast, on this side almost unbroken, extends a low flat plain from 15 to 20 miles in breadth. On the north it is bordered by great steppes, the surface of which is below that of the ocean, and the country eastward is occupied by the desert plateau of Ust-urt, and the sandy deserts of the Turkomans. During the Post-Pliocene period the waters of the Caspian extended in the shape of a wide gulf north, towards the mouth of the Kama (q.v.), and through a narrow strait between the Balkan Mountains, over the steppes of the lower Amu-Daria, embodying Lake Aral, whose level is now 248 feet higher than the Caspian's, while that of the Caspian is 97 feet below the level of the Black Sea. At a still earlier period it was connected with the Black Sea by the channel of the two Manytch rivers (see CAUCASUS). The Caspian Sea has no tides, but its navigation is dangerous because of violent storms, especially from the south-east. Its level differs much at different seasons, owing to the variable amount of water brought by its tributaries and the extent of evaporation. It is very shallow in the north, where a depth of 14 feet is reached only at a distance of no less than 10 miles, and that of 12 fathoms (72 feet) at a distance of 130 miles from the mouth of the Volga. In its middle it is intersected by a submarine ridge which continues the main Caucasus chain from the Apsheron peninsula towards the ESE., and divides the Caspian into two deep basins. The greatest depth found in the northern basin is 2526 feet, and in the southern (close by the southern shore) 3006. The Caspian receives the waters of a number of large rivers, of which the greatest is the Volga. The Ural, the Emba, the Terek, the Kura, and the Atrek also fall into it. The water is salt, but much less so than that of the ocean. The northern parts of the Caspian are covered with ice during winter. It abounds in fish, and very valuable fisheries are carried on, especially for sturgeon and salmon. Besides many species of its own, it has several species of fish in common with the Black Sea, the Arctic Ocean, and Lake Aral; this suggests that the separation of the Caspian from the Black Sea took place in the earlier period of the Post-Pliocene period, or perhaps during the Pliocene. By a canal uniting the upper tributaries of the Volga with those of Lake Ladoga and the Duna, the Caspian is united with the Baltic Sea. The sea is now surrounded on three sides by Russian territory, the southern shore still remaining Persian. The Russians have a fleet stationed upon it, and lines of steam-packets. The chief Russian towns upon its shores are Astrakhan, Derbend, Baku, and Krasnovodsk (q.v.), from near which a railway runs by Askabad towards Merv, and thence to Samarkand in Turkestan. Steamers ply between Krasnovodsk and Baku, which is connected by rail with Poti on the Black Sea. Balfush, Reshd, and Astrabad are Persian towns.
The Caspian Sea was known to the Greeks and Romans. According to Strabo, it derived its name from the Caspii, a tribe inhabiting its western shores. The name Caspian was afterwards limited to the western portion of the lake—the eastern being designated the Hyrcanian Sea.