The reader will remember that this moment, with the loss of the frontier fortresses Longwy and Verdun, and the evidence of demoralisation which that afforded, was also the moment of the September massacres and of the horrors in Paris. Dumouriez and the mixed French force which he commanded had been ordered by the Ministers of War to hold the line of the Argonne against which the Allies were marching. And here it is well to explain what was meant in a military sense by this word “line.” The Argonne is a long, nearly straight range of hills running from the south northward, a good deal to the west of north. Their soil is clay, and though the height of the hills is only three hundred feet above the plain, their escarpment or steep side is towards the east, whence an invasion may be expected. They are densely wooded, from five to eight miles broad, the supply of water in them is bad, in many parts undrinkable; habitation with its provision for armies and roads extremely rare. It is necessary to insist upon all these details because the greater part of civilian readers find it difficult to understand how formidable an obstacle so comparatively unimportant a feature in the landscape may be to an army upon the march. It was quite impossible for the guns, the wagons, and therefore the food and the ammunition of the invading army, to pass through the forest over the drenched clay land of that wet autumn save where proper roads existed. These were only to be found wherever a sort of natural pass negotiated the range. Three of these passes alone existed, and to this day there is very little choice in the crossing of these hills. The accompanying sketch will explain their disposition. Through the southernmost went the great high road from the frontier and Verdun to Paris. At the middle one (which is called the Gap of Grandpré) Dumouriez was waiting with his incongruous army. The third and northern one was also held, but less strongly. The obvious march for an unimpeded invader would have been from Verdun along the high road, through the southern pass at “Les Islettes,” and so to Chalôns and on to Paris. But Dumouriez, marching down rapidly from the north, had set an advanced guard to hold that pass and was lying himself with the mass of the army on the pass to the north of it at Grandpré. Against Grandpré the Prussians marched, and meanwhile the Austrians were attacking the further pass to the north. Both were forced. Dumouriez fell back southward to St. Menehould. Meanwhile Kellermann was coming up from Metz to join him, and all the while the main pass at “Les Islettes,” through which the great road to Paris went, continued to be held by the French. [Illustration: Sketch Map, showing the turning of the positions on the Argonne and the Cannonade at Valmy, September 1792.]