In all probability, the Wall would be surmounted by a battlement of not less than four feet in height, and as this part of the structure would be the first to fall into decay, Bede’s calculation was probably irrespective of it. This, however, only gives us a total elevation of sixteen feet. Unless we reject the evidence of Ridley and Erdeswick, we must admit, even after making due allowance for error and exaggeration, that the Wall, when in its integrity, was eighteen or nineteen feet high. This elevation would be in keeping with its breadth. The thickness of the Wall varies considerably; in some places it is six feet, in others nine feet and a half.[18] Probably the prevailing width is eight feet, the measurement given by Bede. The frequency with which the thickness of the Wall varies, favours the idea that numerous gangs of labourers were simultaneously employed upon the work, and that each superintending centurion was allowed to use his discretion as to its width. The northern face of the Wall is continuous, but the southern has numerous outsets and insets measuring from four to twelve inches, at the points, doubtless, where the sections of the different companies joined. [Sidenote: THE NORTH FOSSE.] Throughout the whole of its length, the Wall is accompanied on its northern margin by a broad and deep FOSSE, which, by increasing the comparative height of the Wall, would add greatly to its strength. This portion of the Barrier may yet be traced, with trifling interruptions, from sea to sea. Even in places where the Wall has quite disappeared, its more lowly companion, the fosse, remains. In some fertile districts the plough has been carried over it in vain; owing to the moisture of the site, the corn sown upon it springs up with undue luxuriance, and is almost uniformly laid prostrate before it can ripen. From this circumstance the ground is frequently retained in grass, while the neighbouring parts are under tillage.[19] The fosse thus more readily catches the eye, and is likely longer to retain its groove-like form than if subjected to the ordinary process of cultivation. When the ditch traverses a flat or exposed country, a portion of the materials taken out of it has frequently been thrown upon its northern margin, so as to present to the enemy an additional rampart. In those positions, on the other hand, where its assistance could be of no avail, as along the edge of a cliff, the fosse does not appear. No small amount of labour has been expended in the excavation of the ditch; it has been drawn indifferently through alluvial soil, and rocks of sandstone, limestone, and basalt. The patient exertion which this involved is well seen on Tepper Moor, where enormous blocks of whin lie just as they have been lifted out of the fosse. The fosse never leaves the Wall to avoid a mechanical difficulty.