The Roman Republic extended its territory chiefly by means of the sea towards the west, south, and east: little was done towards extending it in the direction, in which Italy and the two peninsulas dependent upon it to the west and east are connected with the great mainland of Europe. The region which lay behind Macedonia was not subject to the Romans, nor yet even the northern slope of the Alps; only the inland region behind the south coast of Gaul had been annexed by Caesar to the empire. Looking to the position occupied by the empire in general, this state of things could not be allowed to continue; the fact that the inert and unstable rule of the aristocracy had been superseded could not but tell with preeminent effect in this sphere of action. Caesar had not charged the heirs of his dictatorial power with the extension of Roman territory on the north slope of the Alps and on the right bank of the Rhine so directly as with the conquest of Britain; but in reality such an enlargement of the bounds suggested itself far more naturally, and was more necessary, than the subduing of the transmarine Celts, and we can readily understand why Augustus took in hand the former and omitted the latter. The task was divided into three great sections--the operations on the northern frontier of the Graeco-Macedonian peninsula, in the region of the middle and lower Danube, in Illyricum; those on the northern frontier of Italy itself, in the region of the upper Danube, in Raetia and Noricum; lastly, those on the right bank of the Rhine, in Germany. Though conducted for the most part independently, the military political measures in these regions had yet an inward connection; and, as they all had their origin from the free initiative of the Roman government, they can only be understood in their success or in their partial failure, when they are looked at from a military and political point of view as a whole. We shall, therefore, in our account of them, follow the connection of place rather than the order of time; the structure, of which they are but parts, is better viewed in its internal compactness than according to the succession of the several buildings composing it. [Sidenote: Dalmatian war.]