We have seen that the disposition of the French armies at the moment when the shock was being delivered through Belgium involved along the frontiers of Alsace-Lorraine the presence of considerable forces.  These, once the operative corner had taken the shock, formed part of the mass of manoeuvre, and were destined in large part to swing up in aid of the men retreating from the Sambre.

But in the very first days of the war, before the main blow had fallen, and when the French General Staff were still in doubt as to precisely where the blow would fall, considerable bodies had been operating in Alsace and over the Lorraine frontier.  The whole range of the Vosges was carried in the second week after the British declaration of war—­that is, between 10th August and 15th August.  Mulhouse was occupied; upon Monday, the 17th of August, Saarburg, the most important railway junction between Strassburg and Metz, was in French hands.  Up to that date, though such comparatively small forces were involved, the French had possessed a very decisive numerical superiority.  It was not destined to last, for there was moving down from the north the now mobilized strength of Germany in this region; and a blow struck against the French left, with no less than four army corps, was speedily to decide the issue upon this subsidiary front.

[Illustration:  Sketch 66.]

This great force was based upon Metz, from which fortress the action will presumably take its name in history.  It stretched upon the 20th of August from the north of Pont-a-Mousson to beyond Chateau Salins.  Before this overwhelming advance the French left rapidly retired.  It did not retire quickly enough, and one portion of the French force—­it is believed the 15th Division (that is, the first division of the 15th Army Corps)—­failed in its task of supporting the shock.

Details of the action are wholly lacking.  We depend even for what may be said at this date upon little more than rumour.  The Germans claimed a capture of ten batteries and of the equivalent of as many battalions, and many colours.  Upon the 21st the whole French left fell back, carrying with them as a necessary consequence the centre in the Vosges Mountains and the right upon the plains of Alsace.  So rapid was the retreat that upon the 22nd of August the Bavarians were at Luneville, and marching on Nancy; the extreme right of the German line had come within range of the forts north of Toul; and in those same hours during which, on that same Saturday, the 22nd of August, the 5th French Army in the north fell back at the news of Namur and lost the Sambre, those forces on the borders of Alsace-Lorraine had lost all the first advantages of their thrust into the lost provinces, had suffered defeat in the first striking action of the war, and had put Nancy in peril.

Nancy itself was saved.  The French counter-offensive was organized on the 23rd of August, at a moment when the German line lay from St. Die northwards and westwards up to positions just in front of Nancy.  It was delivered about a week later.  That counter-offensive which ultimately saved Nancy belongs to the next volume, for it did not develop its strength until after Sedan Day, and after the end of the great sweep on Paris.