On emerging from the plains of Champagne, at Epernay, the Marne flows through the plateaus of the Ile de France as far as Paris, and the country along its banks changes its aspect. Instead of the wide valley which seems one with the immense bare plain, the stream, breaking out a path for itself through the solid mass of the plateau, has cut a gash from 500 to 2000 metres in width, which turns and winds in graceful and ever-changing curves. Thus, although its general course is from east to west, the trend of the walls of the valley constantly changes and bears toward every point of the compass in turn. Moreover, these walls, intersected by the ravines and valleys of numerous tributary streams, are cut up into capes, bastions, and deep hollows. Finally, the cliff from whose summit the plateau overlooks the valley, and whose average height is about 150 metres, at times rises steeply from the lowland, and again is broken up into terraces following the different strata of which it is composed. Thus, although the topographical elements are simple enough, they lend themselves to an ever-changing combination of forms, which gives to the landscape its great charm, and at the same time offers some formidable advantages of various kinds from a military standpoint. [Sidenote: The placid Marne.] [Sidenote: The Marne easy to cross.] The bright green ribbon of the Marne winds along the valley bottom. The placid stream, about a hundred metres wide and broken here and there by islets, wanders from one bank to the other, lined by poplars and willows. On either side of its limpid waters are broad fields, whose delicate greenery frames the sparkling line of the river, which forms a by no means impassable obstacle. In the days just preceding the German offensive of July 15, American patrols constantly crossed between Chateau-Thierry and Mezy, and picked up prisoners and information on the northern bank. In like manner, during that offensive the attacking German troops were able without great losses to cross the Marne and attack the defenders on the southern bank. To be sure, the Allied air-men made their life a burden by keeping up an incessant bombardment of the bridges, large and small. [Sidenote: Fierce fighting on the slopes.] But the real obstacle which this valley offers is found in the slopes which dominate it, and it was there that the fiercest fighting took place until the day when the French and Americans, having thrown the enemy back across the river, scaled the cliffs of the right bank on his heels and dislodged him therefrom. In this neighborhood there were two sectors of terrific fighting--that of Chatillon-Dormans upstream, and that of Chateau-Thierry below. [Sidenote: A wide valley with steep slopes.] [Sidenote: The vine-growing district.]