The Roman Army, 31 BC–AD 337: A Sourcebook

82 The Roman Army
fighting at the current limits of Rome’s direct control, may also have
served to improve communications and to direct and control traffic;
the gates in Hadrian’s Wall allowed Roman roads to run northwards
and there were camps beyond the wall. It is also possible that a barrier
subsequently used for defensive purposes was originally contructed for
quite different reasons. Indeed the eventual frontiers of the empire may
have been simply where Roman advance had temporarily faltered for
a variety of reasons, with no overall plan. So, it is unsafe to argue that
a strategy of ‘defence in depth’ had emerged by the early third century,
or that Rome had given up ideas of further conquests; the annexation
of Mesopotamia by Septimius Severus shows that imperial military
ambitions still flourished.
At all times of course Roman troops wherever they were stationed
acted as an army of occupation, keeping order among subject peoples.
But it must be emphasized that part of their role was to defend Roman
sovereignty against outside threat, and that this was probably of greater
significance by the end of the second century. Frontier zones or lines do
indicate that the areas directly controlled by Rome were now more
precisely demarcated. Significantly, by the early third century the main
concentration of troops was on the Rhine and Danube, rather than in
the east, the last area to see expansion. It was politically important for
emperors to maintain the territorial integrity of the empire, and they
should be credited with a wish to protect the peace and prosperity of
their peoples, many of whom now served in the army, while the provincial
upper classes increasingly contributed senators. Plautius Silvanus
celebrated his military achievements in Moesia not merely as victorious
conquest but as consolidation of the peace of his province (ILS 986). For
discussion, see Mann (1974, 1979); Luttwak (1976); Isaac (1992).
142 Tacitus (1st–2nd C.AD), Annals 4. 5
Italy was protected by two fleets, one on each of the seas on either side,
at Misenum and Ravenna; the adjacent coast line of Gaul was protected
by the warships which Augustus had captured in his victory at Actium
and stationed at Forum Julii with a strong complement of rowers. Our
principal force, however, was close to the river Rhine, where eight legions
were stationed as a defence against the Germans or the Gauls. The
Spanish provinces, recently subdued, were in the charge of three legions.
King Juba had received the people of Mauretania as a gift of the Roman
people. The rest of Africa was guarded by two legions, and Egypt by
an equal number. Then all the great sweep of territory from the borders
of Syria to the river Euphrates was kept under control by four legions;