Then came an era when the Imperial purple became the prize of successful generals acclaimed by their legions; and the frontier armies, themselves largely formed out of Teutonic or other semi-“barbarian” tribes, found themselves face to face with new barbarian hordes which for another century and a half they held in check. But the tremendous external pressure on frontiers so vast made it imperative that the Government should be somewhat decentralised. At the end of the third century Diocletian parted the empire into four great divisions. The new system could not endure; Constantine the Great again became sole emperor. Under him Christianity was at length adopted as the state religion; the Church herself became a fundamental factor in the political system; and the political centre of gravity was transferred from Rome to Byzantium. [Sidenote: Beginning of Byzantium] Again the empire was partitioned, and then, for a brief while before the end of the fourth century, united again under Theodosius. But the end was at hand. For a few years the great general Stilicho held the Teutonic Goths at bay in Italy, while Vandals and Sueves poured through Gaul into Spain. Then, early in the fifth century, Stilicho died. Alaric led his conquering hordes to the gates of Rome, and sacked the Eternal City. His successor, Ataulf, took his Goths away, to drive the Vandals out of Spain into Africa, and set up a great western kingdom on their own account. But after the Goths, fresh barbarians swarmed in--Tartar Huns under Attila, who wrought huge devastation and then vanished for ever; then fresh Teutonic armies, which took possession of Italy, though in the East the Empire still held its own. And in Gaul the (German) Franks under their king, Clovis (Chlodwig, Ludwig), established the dominion which was to give its name to France when the Frankish element had almost passed out of the country. Far-away Britain had already been abandoned, and was falling a prey to the Saxons and the Angles, the “English” who were driving the earlier Celtic inhabitants before them into the mountain fastnesses of the west and north. Again, in the East, in the sixth century, the empire centred at Byzantium asserted its power. Justinian is memorable for that great codification of Roman Law on which the legal systems of half the jurists in Europe have been based. His reign is famous also for the exploits of his brilliant general, Belisarius, who destroyed the Vandal kingdom in Africa, restored the Imperial rule in Italy, and recovered provinces in Asia which had been in danger of falling into the grip of the now aggressive rulers of Persia. But in the West, the success was only temporary. Under pressure of Tartar or Slavonic hosts from the East, a fresh Teutonic swarm, the Lombards, entered Italy and mastered the North. The significance of Rome now lay in the supremacy of her pontificate, unacknowledged in the East.