Alexander's empire temporarily established Hellenic institutions throughout western Asia and some of the provinces remained superficially Greek until they were incorporated in the Roman Empire and ultimately became part of early Christendom. On the whole, however, from the time of Alexander the elimination of European blood, classic culture, and, finally, of Christianity, went on relentlessly. By later Roman times the Aryan language of the Persians, Parthians, and people of India together with some shreds of Greek learning were about all the traces of Europe that were to be found east of the oscillating boundary along the Euphrates. The Roman and Byzantine Empires struggled for centuries to check the advancing tide of Asiatics, but Arab expansions under the impulse of the Mohammedan religion finally tore away all the eastern and southern coasts of the Mediterranean Sea, while from an Arabized Spain they threatened western Europe. With the White Man's world thus rapidly receding in the south, a series of pure Mongol invasions from central Asia, sweeping north of the Caspian and Black Seas, burst upon central Europe. Attila and his Huns were the first to break through into Nordic lands as far as the plains of northern France. None of the later hordes were able to force their way so far into Nordic territories, but spent their strength upon the Alpines of the Balkans and eastern Europe. Eastern Germany, the Austrian states, Poland, and Russia had been Nordic lands before the Slavs emerged after the fall of Rome. Whether the occupation of Teutonic lands by the Wends and Slavs in eastern Europe was an infiltration or a conquest is not known, but the conviction is growing that, like other movements which preceded and followed, it was caused by Mongoloid pressure. That the western Slavs or Wends had been long Nordicized in speech is indicated by the thoroughly Aryan character of the Slavic languages. They found in the lands they occupied an underlying Teutonic population. They cannot be regarded as the original owners of Poland, Bohemia, Silesia, or other Wendish provinces of eastern Germany and Austria. The Teutonic Marcomanni and Quadi were in Bohemia long before the Czechs came in through the Moravian Gate in the sixth century. Pomerania and the Prussias were the home of Teutonic Lombards, Burgunds, Vandals, and Suevi, while the Crimea and the northwestern coast of the Black Sea were long held by the Nordic Goths, who, just before our era, had migrated overland from the Baltic by way of the Vistula. No doubt some of this Nordic blood remained to ennoble the stock of the later invaders, but by the time of Charlemagne, in the greater part of Europe east of the Elbe, the Aryan language was the only bond with Europe.