2. But beyond the empire to the north, advancing upon it like the multitudinous waves of the ocean on an exposed coast, lay the ever-battling legions of the northern tribes in their three great divisions of the Teutonic, Slavic, and Finnish races. If Roman society suffered throes of distress, its condition was peace compared with the instability which may be said to have been the very life of these tribes. Once at least in every century they gather themselves up for a concentrated effort against the empire whose rich civilisation lies stretched out before them as a continual prey. After the failure of Arminius to construct a German kingdom, and of Marobod to construct a Suevian, in the time of Augustus, Decebalus, in the time of Trajan, makes another effort in behalf of his Dacians. But here the great Roman general forces barbarism to retreat, and plants a fresh citadel in its very stronghold by establishing a province north of the Danube. Then there is comparative tranquillity for sixty years. It seems as if these two generations were offered by divine Providence to the empire yet in its unbroken strength as a time for its pacific conversion, which if it had accepted, the eruption of the northern nations might for ever have been kept back by the unity which religious conviction would have bestowed on civilisation, and the fresh and living force which it would have imparted to society not yet exhausted by despotic power. But with Marcus Aurelius the empire turns definitively away. A new religious revolution under Odin in Scandinavia had wakened up with redoubled force the destroying energy of barbarism. The Goths had migrated from Sweden to the Black Sea; all the tribes in the interval had been displaced and dashed upon each other by this removal. The war of the Marcomans occupied during eighteen years, from 162 to 180, the whole forces of the empire; Rome was obliged even to arm its slaves, and Italy feared an invasion more terrible than that of the Cimbri, which it cost Marcus Aurelius his life to avert. Again, during the captivity of Valerian, another grand assault of the northern tribes takes place. The Franks attack western, the Alamans eastern Gaul; they pass the Alps and advance to Ravenna, while Alamans and Sarmatians throw themselves upon Pannonia, and the Goths seize upon Thrace and Greece. The emperors Claudius, Aurelian, and Probus are the saviours of Rome from this new flood. Of the last of these it is recorded that he dealt successively with Franks, Burgundians, Alamans, Vandals, the Bastarnæ, and the whole barbarian brood: and seventy cities raised from their ruins, and fortifications repaired upon a line of fifteen hundred miles, were the fruits of his victories.(271)