Note 4 — Chapter IV · A New Interpretation

Upon the general inadequacy of rivers as frontier lines there are some good remarks by Lord Curzon, The Romanes Lecture: Frontiers, Oxford, 1908, p. 20 ff., and Miss Ellen Semple, Influences of Geographic Environment, New York, 1911, p. 360 ff. It is only rarely in fact that a large river actually forms a boundary line; exceptions like the Rio Grande, a short stretch on the upper St. Lawrence, the La Plata, the Amur, the lower Aras and the lower Danube, only emphasize the rareness of the phenomenon. Besides, rivers play a relatively slight rôle in military history; they can be crossed only too easily, if not in the direct face of the foe, as at Wagram, Fredericksburg, or the Yalu, at least at some point above or below. In the long course of the German wars the river Rhine plays a most subordinate part; battles were fought freely on one side or the other, but none, that we have noted, for its actual passage, unless an exception be made of an action of Drusus in 12 B. C., which Dio 54, 32, 1, thus describes: “Having watched for the Kelts until they were crossing the Rhine he cut them to pieces.” This may have been a battle for a crossing, but it seems much more plausible that it was a mere attack from an ambuscade, the river playing merely an incidental part. Of course these remarks apply only to the period of mobile armies. In modern trench warfare, with solid lines hundreds of miles long, any ditch, even such as the trifling Yser canal, may be a formidable obstacle; but this is a wholly new phase of military tactics.