Coeln-Berlin, the marches of Brandenburg, East and West Prussia—­in fact, all the now Germanized lands to the east of the Elbe—­owe their Teutonic character to a great reflux, a reconquest so to speak, which is barely mentioned in the usual textbooks of German history, yet which is one of the most noteworthy phenomena in the development of modern Europe.  At the beginning of the fourth century German tribes (German in the widest sense of the term) occupied the broad expanse from the Rhine to the Dwina and the head-waters of the Dnieper.  A century later they had receded as far as the Vistula.  Still another century later, about 500, the German linguistic domain was bounded on the east by the Ens, the Bohemian Hills, the upper Main, the Saal and the Elbe.  The downfall of the Thuringian kingdom was the occasion of Slavic encroachments even on the left bank of the Elbe between Stendal and Lueneburg.  This German recession, which boded the Slavization not only of Eastern but also of Central Europe, was due to various causes, many of which are veiled in the impenetrable darkness which still hangs over the early Middle Ages.  The chief causes were undoubtedly the Germanic migration over the Roman world and the settlement of the Franks in Northern Gaul and the Saxons in England.

But with the Carolingian dynasty came a new era.  Charles Martel, Pepin and Charlemagne aspired to universal monarchy.  Not content with France, Northern Spain, Italy and Germany proper, Charlemagne, as we have already seen, recaptured the middle Danube.  His successors in Germany, the Saxon, Franconian and Swabian emperors, continued the impulse, but gave it in the main a different direction.  Instead of moving toward the south-east, where they would have encountered stubborn opposition from the already compact Hungarian nationality, they chose for their field of colonization (or recolonization) the east and north-east.  Throughout the eleventh, twelfth, thirteenth and fourteenth centuries we observe a strong and unremitting tide of German peasants, burghers and knights flowing through and over Brandenburg, Pomerania, Mecklenburg, Silesia, the Prussian duchies, and even into Lithuania, Curland, Livonia and Esthonia.  We have here an explanation of the want of interest taken by the Germans in the Crusades.  While the kings of England and France, the barons and counts of Brabant and Italy, were wasting their substance and the blood of their subjects in hopeless attempts to overthrow Mohammedanism on its own ground, the Germans were laying the foundations—­unconsciously, it is true—­of a new empire.  The lands wrested from the Slaves were to be the kingdom of Frederick the Great.  The work was done thoroughly, almost as thoroughly as the Saxon conquest of Britain.  The Obotrites, Wiltzi, Ukern, Prussians, Serbs and Vends were annihilated or absorbed.  The only traces of their existence now to be found are the scattered remnants of dialects spoken in remote villages