You know enough about strategy to be aware that when von Kluck retreated he left the right wing of von Buelow's army exposed. You may be certain that General Joffre ordered this wing to be attacked without delay. When the enemy perceived that his right was in danger he made a desperate effort, which lasted from 7th September to 10th September, to pierce the French centre, to the west and east of a place known as La Fère Champenoise,[109] on one of the upper streams of the Grand Morin. We must pay particular attention to the fighting in this region, for the result of it was to set the whole German line retreating. [Illustration: General Foch.] Look at the little map on the next page and find the town of Sézanne. From this place the 9th French Army extended for about twenty miles to the east. It was a newly-created army, which had not yet been engaged; and it was under the command of General Foch,[110] a brilliant writer on the art of war. It was now to be seen whether he was as good in the field as he had proved himself to be in the study. On the 8th of September Foch's army was violently attacked by the famous German Guard, and his right was forced back a few miles. Early next morning he made a further retreat, and at the same time drew back his left, so as to maintain his line. Although he had retreated he was full of fight, and he ordered an attack to be made the same day. [Illustration] To the north of Sézanne you will see a region known as the Marshes of St. Gond. This stretch of swampy ground was the scene of a great fight which forced the retreat of the German centre; we must, therefore, look at it more closely. In the plateau to the north of Sézanne is a basin of clay, ten miles long from east to west, and varying in breadth from one to two miles. The streamlets which give rise to the Petit Morin run across it, and the whole ground was formerly a bog. It has long been reclaimed; the streamlets run in deep ditches, and some of them have been turned into canals. In ordinary dry weather most of the district is open country, with a good deal of pasture for cattle, though here and there traces of its marsh character are still to be seen in the rush-covered levels. After a few hours of heavy rain the streams overflow, and flood the roads and tracks; the ground becomes a swamp, and the highways are deep in mire.