This division of the Empire is the great political feature of the fifth century; but the fate of the two Empires was widely different. ♦Enemies of Rome.♦ From the very beginning of the Empire, Rome had had to struggle with two chief enemies, in the East and in the West, in Europe and in Asia, the nature of whose warfare was widely different. ♦Rivalry with Parthia and Persia.♦ In the East she had, first the Parthian and then the regenerate Persian, as strictly a rival power on equal terms. This rivalry went on from the moment when Rome stepped into the place of the Seleukids till the time when Rome was cut short, and Persia overthrown, by the Saracenic invasions. But, except during the momentary conquests of Trajan and during the equally momentary alternate conquests of Rome and Persia in the seventh century, the whole strife was a mere border warfare which did not threaten the serious dismemberment of either power. This and that fortress was taken and retaken; this and that province was ceded and ceded back again; but except under Trajan and again under Chosroes and Heraclius, the existence and dominion of neither power was ever seriously threatened. ♦Rivalry with Persia passes on to the Eastern Empire.♦ The Eastern Empire naturally inherited this part of the calling of the undivided Empire, the long strife with Persia. At the other end of the Empire, the enemy was of quite another kind. ♦Teutonic incursions in the Western Empire.♦ The danger there was through the incursions of the various Teutonic nations. There was no one Teutonic power which could be a rival to Rome in the same sense in which Persia was in the East; but a crowd of independent Teutonic tribes were pressing into the Empire from all quarters, and were striving to make settlements within its borders. The task of resisting these incursions fell of course to the Western Empire. ♦No Teutonic settlements in the Eastern Empire.♦ The Eastern Empire indeed was often traversed by wandering Teutonic nations; but no permanent settlements were made within its borders, no dismemberment of its provinces capable of being marked on the map was made till a much later time. But the Western Empire was altogether dismembered and broken in pieces by the settlement of the Teutonic nations within it. The geographical aspects of the two Empires during the fifth century are thus strikingly unlike one another; but each continues one side of the history of the undivided Empire. It will therefore be well to trace those two characteristic aspects of the two Empires separately. We will first speak of the Teutonic incursions, through which in the end the Western Empire was split up and the states of modern Europe were founded. We will then trace the geographical aspect of the long rivalry between Rome and Persia in the East. § 3. _The Teutonic Settlements within the Empire._