ribed in connection with the battles of
the Marne, and it is the western section of this line which now demands
consideration. Just as the River Marne was taken as a basis for the
consideration of the topography of the battles that centered round the
crossing of the Ourcq, Grand Morin, Petit Morin, and the Marne, so the
Aisne is naturally the most important determinant in the problems of its
crossing.

The River Aisne rises in the Argonne, southwest of Verdun. Through the
Champagne region its banks are of gradual slope, but shortly after it
passes Rethel, on its westerly course, the configuration changes
sharply, and at Craonne the bluffs overlooking the river are 450 feet
high. It is easy to see what an inaccessible barrier is made by such a
line of cliffs. For forty miles this line of bluffs continues, almost
reaching to Compiegne, where the Aisne enters the Oise. Not only are the
banks of the Aisne thus guarded by steep bluffs, but the character of
those bluffs is peculiarly fitted for military purposes. For long
stretches along the north side the cliffs stand sheer and have spurs
that dip down sharply to the valley. The ridge, or the top of the bluff,
which looks from below like the scarp of a great plateau, lies at an
average of a mile or more from the stream. Many of these spurs jut out
in such a way that if fortified they could enfilade up and downstream.
To add to the military value of such a barrier the edge of the scarp is
heavily wooded, while the lower slopes are steep and grassy, with small
woods at irregular intervals. Even from the high ground on the south
bank of the stream, the top of the plateau on the north cannot be seen,
and from below it is effectually cloaked.

Two tributaries are to be considered in this river valley which thus
forms so natural a post of defense. Both flow in from the south, the
Suippe, which joins the main stream at Neufchatel-sur-Aisne and the
Vesle, on which stands the ancient city of Rheims. This river joins the
Aisne a little over seven miles east of Soissons, which is itself twenty
miles east of Compiegne.

The line taken by the German armies for their stand was not the river
itself, but the northern ridge. At no place more than a mile and a half
from the river, it was always within gunfire of any crossing. Every
place of crossing was commanded by a spur. Every road on the north bank
was in their hands, every road on the south bank curved upward so as to
be a fair mark f