Caspian Sea
The wide and endorheic Caspian Sea has a north–south orientation and its main freshwater inflow, the Volga River, enters at the shallow north end. Two deep basins occupy its central and southern areas. These facts lead to horizontal differences in temperature, salinity, and ecology. The Caspian Sea spreads out over nearly 750 miles (1,200 km) from north to south, with an average width of 200 miles (320 km). It covers a region of around 149,200 square miles (386,400 square km)—bigger than the region of Japan—and its surface is about 90 feet (27 meters) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on earth after Lake Baikal (−1,180 m, −3,871 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size.
Russian conquest of Central Asia
The area was bounded on the west by the Caspian Sea, on the north by the Siberian forests and on the east by the mountains along the former Sino-Soviet border. The southern border was political rather than natural. It was about 1300 miles from north to south, 1500 miles wide in the north and 900 miles wide in the south. Because the southeast corner (Kyrgyzstan and Tajikistan) is mountainous the flat desert-steppe country is only about 700 miles wide in the south. Using modern borders, the area was 1,545,730 square miles, about half the size of the United States without Alaska. On the east side two mountain ranges project into the desert. Between them is the well-populated Ferghana Valley which is approximately the 'notch' on the west side of Kyrgyzstan. North of this projection the mountain-steppe boundary extends along the north border of Kyrgyzstan about 400 miles before the mountains turn north again.