compelled to turn it, to make his attack on a side of it or in rear. Now to prevent this being easily done, points d’appui were sought for these lines, which should give them a certain degree of support on the side, such as the Rhine and the Vosges give the lines in Alsace. The longer the front of such a line the more easily it can be protected from being turned, because every movement to turn it is attended with danger to the side attempting the movement, the danger increasing in proportion as the required movement causes a greater deviation from the normal direction of the attacking force. Therefore, a considerable length of front, which can be made unassailable, and good flank-supports, ensure the possibility of protecting a large space of territory directly from hostile invasion: at least, that was the view in which works of this class originated; that was the object of the lines in Alsace, with their right flank on the Rhine and the left on the Vosges; and the lines in Flanders, fifteen miles long, resting their right on the Scheldt and the fortress of Tournay, their left on the sea.
But when we have not the advantages of