But even after these transferences Dacia remained an advanced position on the left bank, covered by mountains and defences, with reference to which it might well be doubtful whether it did more to promote or to impede the general defensive attitude of the Romans. Hadrian, in fact, had thought of giving up this territory, and so regarded its incorporation as a mistake; after the step had once been taken, there certainly preponderated the consideration, if not of the lucrative gold mines of the country, at any rate of the Roman civilisation rapidly developing itself in the region of the Marisus. But he caused at least the superstructure of the stone bridge of the Danube to be removed, as his apprehension of its being used by the enemy outweighed his consideration for the Dacian garrison. The later period released itself from this anxiety; but the eccentric position of Dacia in relation to the rest of the frontier-defence remained. The sixty years after the Dacian wars of Trajan were for the Danube lands a time of peace and of peaceful development. No doubt there was never entire quiet, particularly at the mouths of the Danube, and even the hazardous expedient of purchasing the security of the frontier from the adjoining restless neighbours, just as was done with Decebalus, by the bestowal of yearly gratuities was further employed;[133] yet the remains of antiquity show at this very time everywhere the flourishing of urban life, and not a few communities, particularly of Pannonia, name as their founder Hadrian or Pius. But upon this stillness followed a storm such as the empire had not yet sustained, and which, although properly but a frontier-war, by its extension over a series of provinces and by its duration for thirteen years shook the empire itself. [Sidenote: Marcomanian war.]