The world's largest lake - the Caspian Sea is situated within the vast continental depression settled over bordering areas of a single Euro-Asia continent.
The most ancient inscriptions related to the Caspian Sea were encountered upon an Assirian ceramic pot, mentioned as the Southern Sea. The Hekatey of Milet's historical and geographic books (VI BC) mentioned this sea as Caspy and Hirkan. The first ethnic name is associated with the name of the Caspy people who were dwelling in southwest coastal areas of the current territory of Azerbaijan. Its second name was originated from Hircan country, which was located in the southeast coastal areas (translated from Persian as "the country of wolves").
These two names of the Caspian Sea were also mentioned by Herodotus (5th century BC). Other ancient authors were also using such names as Alban (in association with the Albanian ethnic name), Stormy and Hirkan names of the sea. Ancient Russian manuscript sources named Caspian Sea as Goy (that means Blue in Mongolian-Turk languages), Kharezm (in association with the Kharezm power located within the area extended from Amu-Darya River lower intercourse up to the Caspian Sea, Khvalin, Darband etc. People that had dwelt around Caspian Sea called it with different names, for example: the Russians - Khvalin, the Tartars - Agh Daniz (White Sea), the Turk people - Kichik Daniz (Small Sea), the Chinese people - Si Hay, and the New west Sea. Venice Ambassador to Iran (1474-1477) A. Kontarini named it as Baku Sea. The Russians used to call the sea Caspian since the 16th century. Other countries around the Caspian Sea called this basin as follows: Caspian (Khazar) in Azerbaijan, (Khazar -Turk speaking people that dwelt within the northwest coastal areas during V-X centuries), Mazandaran - in Iran, as well as Caspian - in Kazakhstan and Turkmanistan. All in all, over 70 names were given to the Caspian Sea by various people who dwelt around the basin in various times.
The formation of the Caspian Sea began 10M years ago, and during this period of time several changes of the sea water level as well as the recurring transgressions and regressions took place. During the Tertiary period (began about 70M years ago) the Ponto-Caspian basin was isolated from the Tethys Ocean and its southern seas and gradually transformed into a stand-alone inland basin. At the Late Pontian and Middle Pliocene time (10M years ago), the vast inland Sarmatian basin, which extended from the Black Sea to the Caspian Sea, was divided into several parts with the stand-alone Caspian Sea. During the Quaternary period (500th years ago), the Caspian Sea was linked to the Black Sea by the Kuma-Manich depression. The fluctuation of the Caspian Sea water level ranged about 300m during the last geological period of time.
Sometimes, sea bottom in the entire North Caspian and partially Middle Caspian sectors underwent subaerial exposure, whereas South Caspian-Lankaran basins remained submerged under the water surface.