[Illustration: Wall of Severus]
The wall was a good defense as long as Roman soldiers remained to guard it. But in process of time—about two centuries after Severus’s day—the Roman empire itself began to decline, even in the very seat and center of its power; and then, to preserve their own capital from destruction, the government were obliged to call their distant armies home. The wall was left to the Britons; but they could not defend it. The Picts and Scots, finding out the change, renewed their assaults. They battered down the castles; they made breaches here and there in the wall; they built vessels, and, passing round by sea across the mouth of the Solway Frith and of the River Tyne, they renewed their old incursions for plunder and destruction. The Britons, in extreme distress, sent again and again to recall the Romans to their aid, and they did, in fact, receive from them some occasional and temporary succor. At length, however, all hope of help from this quarter failed, and the Britons, finding their condition desperate, were compelled to resort to a desperate remedy, the nature of which will be explained in the next chapter.
[Footnote 1: For some account of the circumstances connected with this war see our history of Alexander, chapter vi.]
Any one who will look around upon the families of his acquaintance will observe that family characteristics and resemblances prevail not only in respect to stature, form, expression of countenance, and other outward and bodily tokens, but also in regard to the constitutional temperaments and capacities of the soul. Sometimes we find a group in which high intellectual powers and great energy of action prevail for many successive generations, and in all the branches into which the original stock divides; in other cases, the hereditary tendency is to gentleness and harmlessness of character, with a full development of all the feelings and sensibilities of the soul. Others, again, exhibit congenital tendencies to great physical strength and hardihood, and to powers of muscular exertion and endurance. These differences, notwithstanding all the exceptions and irregularities connected with them, are obviously, where they exist, deeply seated and permanent. They depend very slightly upon any mere external causes. They have, on the contrary, their foundation in some hidden principles connected with the origin of life, and with the mode of its transmission from parent to offspring, which the researches of philosophers have never yet been able to explore.