the Chaldeans, also a Semitic tribe, re-established Babylon and made that city the most important capital of that day. Nebuchadnezzar, the best known of their Kings, encouraged the study of science, and our modern knowledge of astronomy and mathematics is all based upon certain first principles which were discovered by the Chaldeans. In the year 538 B.C. a crude tribe of Persian shepherds invaded this old land and overthrew the empire of the Chaldeans. Two hundred years later, they in turn were overthrown by Alexander the Great, who turned the Fertile Valley, the old melting-pot of so many Semitic races, into a Greek province. Next came the Romans and after the Romans, the Turks, and Mesopotamia, the second centre of the world's civilisation, became a vast wilderness where huge mounds of earth told a story of ancient glory.
