This early line of detached forts, less than 3000 yds. from the
enceinte, was completed by the Germans with forts of polygonal type
such as Fort Prinz August. The hill of St Quentin (fig. 46), a very
important point, was converted into a fortified position, with two
forts and connecting parapets, and a communication running north to
Fort Alvensleben.
The arrangement of wing batteries in connexion with the forts can be
clearly noted at Fort Manteuffel. These are reinforced by other
batteries either for the defence of the intervals or to dominate
important lines of approach such as the valley of the Moselle (canal
battery at Montigny). To these were added later armoured batteries.
There are also infantry positions, shelters and magazines in connexion
with this line.
Finally some new forts of modern type were commenced in 1899 at about
9000 yds. from the place.
Fortresses.
Leaving out of consideration at present the strategic use of groups of
fortresses, the places which, as mentioned above, are intrinsically
worth being defended as fortresses are:--
(a) Centres of national, industrial or military resources.
(b) Places which may serve as _points d'appui_ for manoeuvres.
(c) Points of intersection of important railroads.
(d) Bridges over considerable rivers.
(e) Certain lines of communication across a frontier.
Examples of (a) are Paris, Antwerp, Lyons, Verdun. Again for (a) and
(b), as is pointed out by Plessix and Legrand, Metz in the hands of the
Germans may serve both as a base of supplies and a _point d'appui_ for
one flank. Strassburg is a bridge-head giving the Germans a secure
retreat across the Rhine if beaten in the plains of Alsace, and an
opportunity of resuming the offensive when they have re-formed behind
the river.
[Illustration: From Plessix and Legrand's _Manuel complet de la
fortification_, by permission.