Achaemenid Impact in the Black Sea

For 200 years, from the second half of the sixth century to the decades before 330 BC, the Persian dynasty of the Achaemenids ruled an enormous empire stretching from the Mediterranean Sea to Afghanistan and India. The Great Kings Dareios I and Xerxes I even tried to conquer Greece and the northern Black Sea territories. Although they failed, parts of Thrace did become part of their dominion for a short period. The question always rises as to why the Great Kings were interested in the western an