If we adopt the theory that the Wall and the Vallum exhibit unity of design, a question of some importance arises—With what view was the Vallum constructed? Hodgson, with much probability, conceives that, whilst the Wall undertook the harder duty of warding off the professedly hostile tribes of Caledonia, the Vallum was intended as a protection against sudden surprise from the south. The natives of the country on the south side of the Wall, though conquered, were not to be depended upon; in the event of their kinsmen in the north gaining an advantage, they would be ready to avail themselves of it. The Romans knew this, and with characteristic prudence made themselves secure on both sides.
PECULIAR CONSTRUCTION OF THE VALLUM.
But, whatever we may conceive to have been the design of the Vallum, the peculiarity of its form will excite the attention of the enquirer, though probably without his arriving at any satisfactory explanation. Supposing, according to the common theory, that the Vallum was an independent fortification, erected long before the Wall, to resist a northern foe, why was not the ditch, as in the case of the stone Wall, drawn along the northern edge of the northern agger? I cannot supply an answer. A similar difficulty meets us on the supposition that it was meant to guard against attack from the other side. Again, what part did the smaller rampart on the south edge of the fosse perform? Possibly it may have been intended as a foot-hold for the soldiers when fighting on this platform against the revolted Britons south of the barrier.
The third, and perhaps the most important, part of the barrier line consisted of the structures that were formed for the accommodation of the soldiery, and for the ready transmission of troops and stores. Neither stone walls, nor ditches, nor earthen ramparts, would alone have proved material impediments to the incursions of the Caledonians—
An iron race, ...
Foes to the gentler genius of the plain.
It is reported that Agesilaus, when asked where were the walls of Sparta, pointed to his soldiers and said, ‘There.’ The Romans placed their chief reliance on the valour and discipline of their armies, though they did not despise the assistance of mural lines. In a foreign country, to which it was difficult to transmit relays of troops, it became a matter of great importance to economize the lives of the soldiery. Hence arose the Wall.
Those portions of the great barrier which yet await our consideration, are the Stations, the Mile-castles, the Turrets, and the Roads.
THE STATIONS.
At distances along the line which average nearly four miles, Stationary Camps (stationes or castra stativa) were erected. These received their distinctive appellation, in contradistinction from those temporary ramparts, which were thrown up when an army halted for a night or for some brief period.