But General von Kluck did not mind the losses he incurred so long as he achieved his purpose. This was clearly his best policy. In the intervals of desperate fighting his men had to undertake long marches at a breakneck pace. For several days together they were without rest or sleep. To some extent they were aided by the entrenchments already dug to guard against an attack from the west. These positions, prepared to protect the head of the German chain of armies remaining in contact with Paris, now proved useful in covering the retirement. Nevertheless, the efforts of the Germans must have been exhausting to the last degree.[17]
Despite that, they were successful in reaching the Aisne in advance of the 6th French army. The latter, it ought, however, to be said, had to operate through a difficult area. From the Ourcq to the Aisne there is a succession of forests. Of these the great forest of Villers-Cotterets extends northwards from the Ourcq to within six miles of Soissons. East of the stretch of forests the country is more open. Given these facts of topography, it is evident that on following the line of the Ourcq, with the object of barring its passage to the enemy, the French had in the forest belt a formidable obstacle. Perceiving that in this lay his chance, General von Kluck hurried as large a part of his force as possible across the Ourcq in order to bar the advance of the French by the forest roads through Villers, and by the comparatively narrow break in the forest belt between Crepy and Pierrefond. He was thus able, notwithstanding that the British were hanging on to and harrying his rear, to hold the outlets against the troops of General Maunoury until he slipped past them.[18]
And once on the Aisne and in touch with his Amiens rearguard, now on the Oise above Compiègne, he was in a position to initiate a complete change in tactics, and, his force being comparatively secure, the other German armies could again fall into line.
Before dealing with those new German tactics, it is advisable briefly to sketch the defence works thrown up by the Germans along their line, because both these defence works and the character of the country are intimately related to the tactics.
As already stated, the highlands of Champagne extend north-west nearly as far as Peronne. They are chalk hills and uplands cut by deep valleys. The most northerly of the valleys is that out of which flows the Somme. Then comes the much wider valley of the Oise. Still farther south is the valley of the Aisne. Between the Oise and the Aisne is a roughly triangular tract of country, its apex at the point where the Oise and the Aisne join. Across the broad end or base of this triangle run the open downs. Towards the narrower end of the area the country becomes broken and hilly, and is covered with great patches of wood and forest.
There is along the north of the Aisne a long wooded ridge, which on its northern edge slopes steeply. But the top of the ridge forms a gentle undulating slope to the south. It is not unlike the top of a rough, slightly tilted table. To a bird's-eye view this top would appear shaped rather like a very coarse-toothed comb, with the teeth jagged and broken. The top, that is to say, runs out on its south side into a succession of promontories, each ending in a round-ended bluff overlooking the Aisne valley. Some of these bluffs jut out close above the river. Others are much farther back. Between them are clefts and side valleys, in which the land slopes up from the bottom of the main valley to the top of the plateau. In the longer clefts, of course, the general gradient is much less stiff than in the shorter ones. Both the tops of the bluffs and most of the clefts are thickly wooded. The bluffs are on an average above 400 feet in height, that in fact being the general elevation of the plateau.
The aspect of the edge of the corresponding plateau on the south side of the valley of the Aisne is exactly similar. Since the bluffs on the opposite sides approach each other in some places and are farther apart in others, the valley varies in breadth from half a mile to two miles. The bottom of the valley is practically flat, and through this flat tract of meadow land the river winds, now near one side of the valley, now near the other. The stream is between fifty and sixty yards wide, but, like all the rivers in this part of France, deep. Where the valley opens out there are villages and small towns. The largest place is the picturesque old city of Soissons.
Now the ridge north of the Aisne extends west to east for some thirty-four miles. At Craonne, its eastern end, it rises to a summit about 500 feet high, and then falls abruptly. There is here, going from the Aisne northwards, a fairly level open gap some three miles wide. South of the Aisne, the same gap extends for about ten miles to Rheims. On each side of the gap rise hillsides clothed with woods. At the crossing of the Aisne is situated the village of Berry-au-Bac. This gap, it will be seen, forms an important feature in the Aisne battle.
Above and behind the hills to the east of the gap, and across the downs, the German entrenchments extended eastward for mile after mile right away to the Argonne. It is apposite here to note that near Rheims the traverse gap widens out and passes right and left round an isolated, hilly mass, lying like an island in a stream. Up the sides of this hilly mass climb the villages of Berru and Nogent-l'Abbesse.
Undoubtedly, one of the surprises of the war was the discovery that the Germans had prepared the positions just described. The preparation must have involved great labour. But it should not be forgotten that from time out of mind one of the chief industries in this part of France is represented by the chalk quarries, out of which is dug the material, known in its prepared state as plaster of Paris. All through Champagne there was, before the war, a considerable German population. Not a few of the plaster quarries had passed into the hands of Germans. The principal quarries are on the steep north slope of the ridge along the Aisne. Cut into the hillsides, these chalk pits present a labyrinth of galleries and chambers, where the quarrymen were accustomed to take their meals and even to sleep. These quarries, numbered by scores, might well form the refuge and stronghold of an army. The region is remarkable, also, for its many natural caves.