But now the valley widens once more as it enters the broad basin of Chateau-Thierry.  It is a beautiful spot, and at the same time, of great military value.  The little town long ago forgot its role of fortress, but has been brutally reminded of it by the violence of the battles that have been fought in its neighborhood.  In the foreground is the wide expanse of fields in the valley bottom; then a suburb of the town enclosed between two arms of the Marne.  Across the river, scaling the slopes of a hill crowned by the ruins of a castle, the town rises, terrace-like, at the mouth of a narrow valley.  The position can be carried by frontal attack only on the heels of a defeated foe, as Napoleon carried it in 1814, and Franchet d’Esperey just a hundred years later.  But in 1918 the Americans had to take Chateau-Thierry in flank, and in order to force their way into the town, had to fight the bloody battles of Vaux, Bouresches, and Etrepilly, which carried them to the north of the town and hastened its evacuation.

[Sidenote:  Military operations difficult.]

What is the nature of the terrain above those steep cliffs which enclose the valley of the Marne?  Does it become more favorable to military operations than the deep depression through which the river flows?  Not by any means.  The surface of the table-land is broken by so many ravines and narrow valleys which descend steeply to the Marne, that it is cut into a multitude of ridges and hillocks amid which it is no longer possible to recognize the original horizontal aspect of the plateau.

[Sidenote:  Heavy impermeable soil.]

[Sidenote:  Hills that are fortresses.]

On the other hand, the strata which lie on the surface—­loam, sandstone, and clayey sand—­make a heavy, impermeable soil, quite infertile, in which it is hard to raise anything, and which is largely given over to woods.  Thus, freedom of movement is impeded by deep ravines, ridges running in all directions, and more or less dense forests; an offensive is difficult, and the defensive easy.  This is true in the immediate neighborhood of Chateau-Thierry, where the ravines of Vaux, Brasles, Charteves, Jaulgonne, and Treloup, and the valley of the Surmelin, slash the plateau on either side of the Marne into fragments—­into forest-topped hillocks which are genuine fortresses, where the struggle was terrific and where the Allies were able to advance only one step at a time:  on Hill 204, west of Chateau-Thierry, in the Bois de Mont St-Pere, the forest of Feze above Jaulgonne, and especially on the spur of the forest of Riz; and south of the Marne, at the broad, wooded bastion of Saint-Agnan and at La Chapelle-Monthodon, where the fighting was so intense from the 15th to the 20th of July.

[Sidenote:  The villages and forests of the table-land.]

[Sidenote:  Genuine mountain battles.]