A fact of special importance can be traced among the causes leading to the supplanting of Low German, the language of the German plain, by High German as the national tongue. The superiority of the highland dialect is due to its greater assimilation of Celtic words. This civilizing influence of Celtic culture is by no means a modern development in Germany. In the proto-historic period it was mainly through contact with the Celts that the Teutons became civilized. This intellectual dependence of the Germans is revealed for the period about 300 B.C. by the then existing civilization, which was entirely Celtic. The history that spans the intervening years naturally brings to mind the influence which French language has always had in Germany. Voltaire’s sojourn at the Prussian court does not rank among forgotten episodes and it was not so long ago that Leibnitz had to resort to French or Latin as the medium of his written expression. The transition from the northern plain of Germany to the high central regions is represented, on the surface, by a zone of intermediate uplands in Saxony, Lusatia and Silesia. This area is characterized linguistically by a transitional form of speech between Low and High German.[6] The similarity, however, of this midland German to High German is observable to the extent to which the rising land over which it is distributed presents analogy to the mountainous region towards which it trends. The transitional dialects include East, Middle and Rheno-Franconian, as well as Thuringian. They occur in the middle Rhineland, the banks of the Moselle, Hesse, Thuringia and Saxony. A bird’s-eye view of the area of German speech shows that the language prevails wherever a well-defined type of dwelling is found. This representative habitation consists of a frame house with an entrance in the middle of one of its long sides. The hearth generally faces the threshold. Barns and outlying buildings do not connect with the main house, but form with it the sides of an open inner yard. German houses can furthermore be subdivided into three distinct sub-types which correspond to the linguistic divisions of Low, Middle and High German. The Saxon sub-type, which rarely rises above a single story, prevails in the northern lowlands, while the Bavarian sub-type dots the mountain districts which resound to High German. Between the two an intermediate sub-type of construction exists in the zone of Middle German. [Illustration: FIG. 7--Sketch map showing relative position of the three main areas in which the dialects of German language are grouped.]