The fluctuations of French in Lorraine since the eleventh century have been studied with great minuteness by Witte.[27] Basing himself on the text of documents examined in the archives of Strassburg, Metz, Nancy and Bar-le-Duc this scholar succeeded in plotting the linguistic divide for the years 1000 and 1500. To these two lines he added the present language boundary as determined from his own field observations. His method consisted in traveling from village to village, usually on foot, and ascertaining personally the predominance of French and German in each locality he visited. Between the eleventh and sixteenth centuries changes along this linguistic boundary appear to have been unimportant. The five intervening centuries are characterized by a slight westerly advance of German. From the sixteenth century to our time, however, the easterly spread of French has been considerable. This change is particularly noticeable in southern Lorraine, as if to show that the gap between the heights of the Moselle and the northern Middle Vosges had provided an outlet for the overflow of the language on German soil. Compared with Lorraine, Alsace has the advantage of greater definiteness as a geographical unit. It is the region of the valley of the Ill which ends at the wall of the Vosges Mountains on the west. Its easterly extension attains the banks of the Rhine. This elongated plain appears throughout history as a corridor through which races of men marched and countermarched. The Alpine race provided it with early inhabitants. Barbarians of northern lineage also swarmed into its fields. Romans subjugated the land in the course of imperial colonization. The province subsequently passed under Germanic and Frankish sway.