THE nomadic Turks swept in from the open steppes in the 11th century and settled themselves in Asia Minor on the ruins of half a dozen cosmopolitan civilizations. Here, before the Turkish conquerors descended, the Hittites(2000 B.C.) first mined, smelted and fashioned iron ore into weapons; the kingdom of Lydia(whose most famous ruler was a man named Croesus) first coined money, and Greeks foughtTrojans over Helen of Troy (though prosaic modern historians insist that they really foughtfor control of the Dardanelles). Near one city alone—Izmir, the ancient Smyrna—are mosaics from the cave where sightless Homer strummedhis lyre, cliff statues of the earth goddess Cybele, and a wall built by Alexander the Great.