Before we do so, however, I will try to give you some idea of the kind of country in front of the French line. Let us imagine that you are travelling westwards from Verdun in early September. Leaving behind you the narrow vale of the Upper Meuse, you traverse an upland country of many ravines and much undergrowth, with here and there small woods and pastures. Then you cross a small stream, and, looking southwards, see the deep woods that stretch towards Bar-le-Duc. The road now rises, and to the northward is the plateau of the Argonne,[100] a long, low ridge of clay, which forms the natural bulwark of north-east France; west of it runs the Aisne and east of it the Aire, a tributary of the Aisne. A small river cuts its way through it in a deep furrow. A French writer says that if we leave out of account the lengthwise furrow through which the river runs, the plateau may be compared with a wave just when it curls and is about to break on the shore. The summits of the plateau range in height from about 450 feet to 1,000 feet.
An extensive forest is always a bar to an invader. In the days when the English were conquering Britain, a very dense and trackless forest, 130 miles long by 30 miles broad, covered that part of South England between the North Downs and the South Downs which we call the Weald. For many years this forest prevented the South Saxons, who had occupied the coast, from pushing their conquests northwards to the Thames. In the same way the Forest of the Argonne checked early invaders of France from the east. No other part of France is so thickly wooded, and in its deep recesses wolves are still found. Two roads and one railway cross it from west to east; but otherwise there are only a few forest paths, which lead nowhere. This difficult region was the scene of desperate fighting during many months of the war.
For a hundred miles to the west of the Argonne stretches a region of chalky moorlands, crossed by many ridges, and broken by heaths, coppices, and fir plantations. This is the Salisbury Plain of France, and men have long foretold that on its dreary levels the Armageddon of Europe would be fought. Still travelling west, we come to the Heights of Champagne, which I have already described. South of the deep-cut valley of the Marne, which, you will remember, marks the southern limit of this chalk plateau, is a region crossed by the Petit Morin and the Grand Morin, both tributaries of the Marne. These tributaries, though not rapid, are so deep that they cannot be forded, but they are well provided with stone bridges. Much of the district through which they flow is well wooded, and dotted with country houses. Round about Sézanne we find rolling downs, and to the north of it the extensive marsh of St. Gond.