Part 4 The Frontiers
The boundary of Caesar's conquests in Gaul extended from Mare Nostrum to Oceanus, from sea to sea, the Mediterranean to the Channel. But in the north and east no such natural boundary was reached. It is clear from Caesar's commentaries that the de facto, if temporary, limit of land under direct Roman jurisdiction was regarded, by Roman and by barbarian, as the Rhine (cf. Caesar, De Bello Callico 4.4; 4.16). So it was to remain for the next forty years until the time of Augustus, for Caesar, preoccupied with more pressing concerns, launched no serious offensive across the Rhine. The river was adopted as a geographically convenient, though arbitrary, divide, which corresponded to no existing cultural distinctions. It attracted none of the paraphernalia of frontier control characteristic of later periods. The army which ensured the security of the newly-won Gallic territory lay back within the province itself, though few of its bases have been positively identified. The threat which this army constituted was, for the most part, sufficient to maintain Gaul's eastern frontier, though tribes did, from time to time, raid across the Rhine into Roman territory. Indeed in 38 BC Vipsanius Agrippa, as governor of Gaul, permitted the philo-Roman Ubii to retain lands on the left bank of the river, to which they had moved from their homeland on the right bank (Tacitus, Cermania, 28).