308 Proceedincfs of the Royal Irkli Academtj. 



Britons, harassed by the Picts and Scots, were advised by the Eomans in the 

 time of Agricola to build a wall : " but raising it," he says, " not of stone, but 

 of sods, made it of no use. However, they drew it for many miles between 

 the two inlets of the sea (the Firths of Forth and Clyde), to the end that 

 where the defence of the water was wanting, they might defend their borders 

 by the help of that rampart. Of which work — there erected, that is of a 

 rampart of extraordinary breadth and height — there are evident remains to 

 this day." 



Another well-known and important march ditch is the well-known 

 Offa's Dyke, erected about a.d. 779 by that king to curb the Celtic Britons 

 from invading Mercia. It runs from Mold in Flintshire, through Denbigh, 

 Montgomery, Shropshire, Hereford, and Monmouth to Chepstow on the Severn, 

 about 120 miles.^ From a memoir by Sir John Maclean, I learn that its 

 construction is similar to the Black Pig's Ditch, namely, a central rampart 

 with a fosse on each side. Certain sections give a base of 40 ft., with a 

 height of from 8 to 15 ft. ; but it varies according to the nature of the ground, 

 and the strategic importance of the situation. In the valley of the Wye it 

 meets precipitous cliffs, and the Dyke runs up to them, but does not exist on 

 the crest. Also, when it dips down into low valleys, which probably were 

 morasses in ancient times, no trace can be found at the lower levels. This is 

 so with the Dane's Cast (the eastern section of the Irish Dyke), at Meigh, 

 Co. Armagh, probably for the same reason. At Highbury a camp lies at the 

 Saxon side ; the Dyke which runs north and south forming its western 

 rampart. This camp is of a curious shape, the similarity of its plan to that of 

 the Dorsey being very remarkable. It may be described as a parallelogram 

 with the opposite obtuse angles rounded off. The course of the Dyke often 

 lies parallel to the Ptiver Wye ; but at one place at least it runs down to the 

 river, which then forms the boundary until the earthworks recommence again. 

 There is also a second Dyke, which at its northern end runs parallel to that 

 of Offa, but more to the east. It goes by the name of Wat's Dyke, and, 

 following the line of the Severn, the river forms the boundary for five miles. 

 In all these early boundary Ditches we find camps as appendages to the 

 trenches, placed on the defenders' side. Up to the present we have no evidence 

 of camps attached to the Irish work, unless we accept as such the Dorsey, 

 and possibly the ring-fort of Ardkillmore in the Cavan " Worm Ditch." I have 

 already shown that from the western side of the Dorsey a foundation of piles, 

 such as those which supported the fortifications where they were constructed 

 through boggy ground, ran out westward towards the line of the Worm 



' Transactions of the Bristol and Gloucestershire Antiquarian Society, vol. vi. 23, and xviii. 19. 



