Arguments have been brought forward by some antiquaries to show that the wall and the vallum by which it is accompanied belong to two different periods; but Dr. Bruce contends that they are both to be considered as forming part of the great engineering work of Hadrian. It consists of a stone wall, or murus, and a wall of earth, or vallum. These two run always near together, but not always parallel. The vallum is likewise rather the shorter, terminating at Newcastle on the east, and at Drumburgh, about three miles from Bowness, the western extremity of the wall.
"The most striking feature in the plan, both of the murus and the vallum, is the determinate manner in which they pursue their straightforward course. The vallum makes fewer deviations from a right line than the stone wall; but as the wall traverses higher ground, this remarkable tendency is more easily detected in it than in the other. Shooting over the country, in its onward course, it only swerves from a straight line to take in its route the boldest elevations. So far from declining a hill, it uniformly selects one.
"For nineteen miles out of Newcastle the road to Carlisle runs upon the foundations of the wall, and during the summer months its dusty surface contrasts well with the surrounding verdure. Often will the traveller, after attaining some of the steep acclivities of his path, observe the road stretching for miles in an undeviating course to the east and the west of him, resembling, as Hutton expresses it, a white ribbon on a green ground. But if it never moves from a right line, except to occupy the highest points, it never fails to seize them as they occur, no matter how often it is compelled, with this view, to change its direction. It never bends in a curve, but always at an angle. Hence, along the craggy precipices between Sewingshields and Thirlwall, it is obliged to pursue a remarkably zigzag course; for it takes in its range, with the utmost pertinacity, every projecting rock."
TRANSVERSE SECTION OF THE ROMAN WALL.
Though no part of the wall now retains its full height, it has been calculated that when entire it was about eighteen or nineteen feet, including the parapet. Its general thickness is about eight feet, though it varies in different parts from six feet to ten and a half feet. It is "throughout the whole of its length accompanied on its northern margin by a broad and deep fosse, which, by increasing the comparative height of the wall, added greatly to its strength. This portion of the barrier may yet be traced, with trifling interruptions, from sea to sea."
LONGITUDINAL SECTION OF THE ROMAN WALL.
The masonry of the wall is somewhat peculiar; it has none of the binding courses of tile which are, in many parts of England and on the Continent, so characteristic of Roman work. No tiles are used in the construction. The outer face of the wall on both sides is formed of squared blocks of stone, usually called ashlar, and the interior of rubble, embedded in mortar. These blocks are about eight or nine inches thick, and ten or eleven wide; their length is considerably more, sometimes as much as twenty-two inches, and tapering to the opposite end, which was firmly bedded into the rubble. The whole rested on a course of large foundation stones.
