The Rhine. The Rhine became the Roman frontier in Caesar's time and, despite Augustus' attempt (12 bc–ad 9) to move beyond it and a somewhat longer (Flavians to c.ad 260) projection of the Upper German frontier to the limes, it remained so until the collapse of the western empire. A strong military presence on the Rhine gave Roman Gaul its shape and its raison d'être (the shielding of Italy); once the legions had gone, the NW provinces were just a burden.
As a means of communication the river, with its tributaries and outlets to the North Sea, was of vital military importance, as between units, between the armies of Germany and Britain, and during campaigns. From 12 bc the Romans maintained a fleet on it, with its headquarters at Colonia Agrippinensis. It was also a great channel of commerce.
Subjects: Classical Studies.