This great military work consisted, in the first place, of an immense fosse or ditch—averaging about forty feet in width, by some twenty in depth—which extended over hill and plain, in one unbroken line, from sea to sea. Behind this ditch, on its southern side, and within a few feet of its edge, was raised a rampart of intermingled stone and earth, strengthened by sods of turf, which measured, it is supposed, about twenty feet in height, and twenty-four in thickness at the base. This rampart, or _agger_, was surmounted by a parapet, behind which ran a level platform, for the accommodation of its defenders. To the southward of the whole was situated the Military Way—a regular causewayed road, about twenty-feet wide—which kept by the course of the Wall at irregular distances, approaching, in some instances, to within a few yards, and in others receding to a considerable extent. Along the entire line there were established, it is believed, nineteen principal stations or forts. The mean distance between each may be stated at rather more than two English miles. Along these intervals were placed many smaller _castella_, or watch-towers. While the continuous rampart seems to have been little more than a well-formed earthen mound, it is probable that many, if not all, of the stations, were either rivetted with stone or entirely built of that material. In some places, it would even appear that the Vallum itself had been raised upon a stone foundation—probably in situations where the ground was low and marshy, and where it was found necessary to form drains beneath the works, to prevent the accumulation of water on their anterior side. [Sidenote: MUTUAL SUPPORT OF THE BARRIERS.] The Barrier of the Upper Isthmus never consisted of more than a single line of fortification. This circumstance may seem to militate against the view that we have taken of the double line of the Southern Barrier. If in the one case the conquered tribes to the south were disregarded, why should they not be so in the other also? We shall not, however, greatly err if we regard the Antonine Wall as but an advanced work of Hadrian’s entrenchment. On this view of the matter, the difficulty is at once removed, for the Lower Barrier would be a sufficient security against danger in the rear. Certain it is, that the southern line was not abandoned when the other was constructed. Several altars have been found on the Lower Barrier inscribed with the name Antoninus Pius.[51] A slab bearing the names of the consuls Sex. Sulpicius Tertullus, and C. Tineius Sacerdos, elicits the following remarks from judge Cay[52]:—