The history of the Roman occupation of Dacia, which lasted from the time of Trajan until it was evacuated by Aurelian,[102] affords little to interest the reader. Dacia was, so to speak, the outwork of the Empire which served to hold the barbarians at bay during its 'decline and fall;' and the country was more prosperous than during the period of its independence, when the tribes were constantly at war with one another and there was no settled government. That the attitude of the barbarians was threatening even a few years after the death of Trajan is, however, more than probable, for his immediate successor, Hadrian, contemplated withdrawing his legions, and destroyed the bridge across the Danube, 118 or 120 A.D. Some writers, indeed, attribute this act to his jealousy of Trajan, others to his hatred of Apollodorus, the architect; but most probably the cause assigned by Dion Cassius, that it was to prevent its being used by the barbarians for making inroads into Mœsia, was the true one.[103] During the reigns of Antoninus Pius and Marcus Aurelius for about half a century, the barbarians were kept in check, although even during that period they had managed to encroach upon the Roman territory. At the beginning of the third century, however, the Roman hold on Dacia began to be very precarious, and we approach the time when the dark veil of the so-called barbarian ages is drawn over the history of Europe. That the Roman emperors had to contend, with very varying fortunes, with barbarous tribes is certain, and that their arms were still frequently successful is proved by the erection of fortresses and towns, named after their emperors, on the borders of their possessions. For example, Caracalla defeated certain barbarous hordes about A.D. 212, and assumed the name of 'Geticus,' but whether the conquered tribes were Dacians or Goths is uncertain. A few years later the Quadi and Marcomanni made inroads into Western Dacia, but they were held in check by the proconsul Varus, who built a tower or fort in close proximity to Trajan's bridge, of which the ruins are still visible to travellers on the Danube, and which has given its name to the modern town of Turnu-Severin. But the Goths, a people of Scandinavian origin, had been for some time previously drawing nearer to the borders of the Roman Empire. Between the beginning of our era and the end of the second century they had spread themselves, associated with the Vandals, in the direction of the Carpathians and the Ukraine, and in the reign of the Emperor Philip (243-249) they made irruptions into Mœsia. In that of Decius they invaded the Roman territory a second time under a chief, Cniva, and, after defeating the Romans and compelling the emperor to flee, they took and sacked Philippopolis. Shortly afterwards Decius met them again, but he was again defeated and slain. The barbarians then retired with their plunder.