In ancient times the Caspian Sea was large than it is now. The ruins of ancient ports and villages have been found as far away as 20 miles (50 kilometers) away from the present shore. In 330 B.C. Alexander the Great reached the southern shore of the Caspian Sea. Ancient mapmakers thought it was part of a sea that stretched all the to the North Pole. The northern limits weren't recognized the A.D. 2nd century. Tsarist Russia secured control of the Caspian Sea during its expansion into the Caucasus and Central Asia in the 18th and 19th centuries. The area was largely undeveloped until oil was discovered around Baku in the late 19th century. By 1900, the Caspian Sea area produced half of the world’s oil.
