On the choice of this position two questions suggest themselves. How was it that the Germans came to pitch upon this place--for there can be no doubt the choice was deliberate[20]--and what operations did they intend to undertake on the strength of its possession? The answers to these questions are in no sense speculations in the secrets of War Offices. Those secrets it would be idle to profess to know. Like the observations made in preceding pages, the answers are deductions from admitted facts and events, perfectly plain to anyone who has knowledge enough of military operations to draw them. Only ignorance can assume that no true commentary can be written concerning a campaign save upon official confidences. As to the German choice of this position, it should not be forgotten that the present war represents the fourth campaign which the Prussians have fought in this area of France. In forming their plans they had, we ought to presume, considered--bearing in mind the difference in military conditions--not only the war of 1870-1, but the campaign of Frederick William II., and the campaign of Blucher in 1814. A little earlier it was said that this arena offers great facilities for defence. The reason is that, since there is here a system of rivers flowing to a conjunction near Paris, it is always open to the defence to attack in superior force between any two of the rivers, while the assailant must, in advancing from east to west, have his forces divided by one or more of the streams. The whole German plan was intended to obviate and to overcome that difficulty, and yet the plan came to grief because, at the moment when their forces were divided by the Marne and by the Grand Morin, the defence were able to attack them in superior force on their extreme right--the vital point--and when the crossing of the rivers made it difficult to meet that attack.[21] Foreseeing, however, the _possibility_, though not accepting the probability, of having to stand for a time on the defensive, the German General Staff, we cannot now doubt, had formed the subsidiary and provisional plan of concentrating, as far as possible and in case of necessity, between two of the rivers--the Oise and the Aisne--in positions which could be held with a minimum of numbers. But this concentration was only preliminary. It was intended to aid the massing on their own right flank of an echelon of reserve formations to be thrown against the left of the Allied forces.