In fact, the traditional Arabic name for the sea itself is Bahr al-Qazwin (Sea of Qazvin)..
The sea has a surface area of 371,000 km Moreover, the Caspian Gates, which is the name of a region in Iran's Tehran province, possibly indicates that they migrated to the south of the sea.The Iranian city of Qazvin shares the root of its name with that of the sea.The sea bed in the southern part reaches as low as 1023 m below sea level, which is the second lowest natural depression on earth after Lake Baikal (-1180 m).The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size. It has a salinity of approximately 1.2% (12 g/l), about a third of the salinity of most seawater.Its northern part, the Caspian Depression, is one of the lowest points on Earth.
The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size.
The sea is estimated to be about 30 million years old. Discoveries in the Huto cave near the town of Behshahr, Mazandaran, (Southern land of Caspian Sea) suggest human habitation of the area as early as 75,000 years ago.
 In classical antiquity among greeks and Persians it was called the Hyrcanian Ocean.
The Caspian Sea, like the Black Sea, Namak Lake, and Lake Urmia, is a remnant of the ancient Paratethys Sea.
This proposal has been submitted to UNESCO in the frame work of the International Geological Correlation Programme (IGCP), a global research facility meant to stimulate knowledge exchange between scientists for all over the world.
Past sea level of the Caspian can give clues to past changes in global climate.