By struggles such as these the contest between the Romans and the Britons was carried on for many generations; the Romans conquering at every trial, until, at length, the Britons learned to submit without further resistance to their sway. In fact, there gradually came upon the stage, during the progress of these centuries, a new power, acting as an enemy to both the Picts and Scots; hordes of lawless barbarians, who inhabited the mountains and morasses of Scotland and Ireland. These terrible savages made continual irruptions into the southern country for plunder, burning and destroying, as they retired, whatever they could not carry away. They lived in impregnable and almost inaccessible fastnesses, among dark glens and precipitous mountains, and upon gloomy islands surrounded by iron-bound coasts and stormy seas. The Roman legions made repeated attempts to hunt them out of these retreats, but with very little success. At length a line of fortified posts was established across the island, near where the boundary line now lies between England and Scotland; and by guarding this line, the Roman generals who had charge of Britain attempted to protect the inhabitants of the southern country, who had learned at length to submit peaceably to their sway. One of the most memorable events which occurred during the time that the Romans held possession of the island of Britain was the visit of one of the emperors to this northern extremity of his dominions. The name of this emperor was Severus. He was powerful and prosperous at home, but his life was embittered by one great calamity, the dissolute character and the perpetual quarrels of his sons. To remove them from Rome, where they disgraced both themselves and their father by their vicious lives, and the ferocious rivalry and hatred they bore to each other, Severus planned an excursion to Britain, taking them with him, in the hope of turning their minds into new channels of thought, and awakening in them some new and nobler ambition. At the time when Severus undertook this expedition, he was advanced in age and very infirm. He suffered much from the gout, so that he was unable to travel by any ordinary conveyance, and was borne, accordingly, almost all the way upon a litter. He crossed the Channel with his army, and, leaving one of his sons in command in the south part of the island, he advanced with the other, at the head of an enormous force, determined to push boldly forward into the heart of Scotland, and to bring the war with the Picts and Scots to an effectual end.