In the campaign of 1645, Turenne was attacked with his army before
Philipsburg by a very superior force. There was no bridge here over
the Rhine, but he took advantage of the ground between the river and
the place to establish his camp. This should serve as a lesson to
engineer officers, not merely in the construction of fortresses, but
of _têtes de pont_. A space should always be left between the fortress
and the river, where an army may form and rally without being obliged
to throw itself into the place, and thereby compromise its security.
An army retiring upon Mayence before a pursuing enemy, is necessarily
compromised; for this reason, because it requires more than a day to
pass the bridge, and because the lines of Cassel are too confined to
admit an army to remain there without being blocked up. Two hundred
toises should have been left between that place and the Rhine. It
is essential that all _têtes de pont_ before great rivers should be
constructed upon this principle, otherwise they will prove a very
inefficient assistance to protect the passage of a retreating army.
_Têtes de pont_, as laid down in our schools, are of use only for small
rivers, the passage of which is comparatively short.