In the West, again, Spain and the south of Gaul had long been Roman when Julius Cæsar started on the campaign which decided the future of Europe, and pushed the Roman frontier forward from the Rhone to the Rhine. The sway of Rome already extended over all the coasts of the Mediterranean, and the accessions made to her dominions during the period of imperial rule were comparatively insignificant. The Danubian and Alpine provinces were won for the Roman Empire by Augustus, Britain was conquered by Claudius, Dacia and Arabia by Trajan, beside the conquests which his successor immediately relinquished. Germania and the kingdom of Parthia permanently withstood the Roman onset, and the construction of the Upper Germanic and Rætian _Limes_ by Domitian was an official recognition of the invincibility of the Germanic barbarians. The counsel of resignation, given by Augustus to his successors out of the fulness of his own bitter experience, warning them to keep the empire within its natural frontiers, _i.e._, the Rhine, Danube, and Euphrates, was practically followed by them, and Hadrian did unquestionably right in breaking altogether with his predecessor’s policy of expansion and refusing to expose the waning might of the empire to a continuous struggle to which it was no longer equal. The great work of the empire, therefore, was not to conquer a world but to weld one into an organic whole, to foster civilisation where it existed and to be the instrument of Græco-Roman civilisation amongst the almost absolutely uncivilised nations admitted into the _Orbis Romanus_: and up to a certain point it actually accomplished this pacific mission, which proceeded with hardly a pause even under the worst of tyrants. Its task, however, varied greatly in various parts of its world-wide field. In the East, permeated with Greek culture, though by no means denationalised, the Romans scarcely made an attempt to enter into competition with this superior civilising agency, and, except as the medium of expression of the Roman magistrates, the Roman language played a very subordinate part there.