GLASGOW ARCHAEOLOGICAL SOCIETY.
sufficient to enable two armed men to pass each other with ease."
When we remember that the North English mwrus is seldom or
never more than 9 feet thick, and is, for the most part, only
6 feet, we are surely warranted in believing that a thickness
of 6 feet at the top would comply with the Vitruvian canon, and
correspond also with the North English example.
Taking the actual 14 feet base along with a theoretical top
of 6 feet breadth, we come to the question of batter. There is
modern authority1 for • holding that sods are not very safe if
built nearer the perpendicular than at a slope of f, that is 3 feet
of rise for every foot of intake or batter. At this, the highest
feasible slope, there would, at the height of 12 feet, be a
restriction of the width by 4 feet on each side, reducing the
width to 6 feet.
But if we were to proceed on the footing that the Roman was
always very cautious not to overstrain his material, and if
adopting a factor of safety we were to assume that the batter
would be something short of the highest feasible, we might
suppose2 that the slope was With that batter the 8 feet of
intake (4 feet on each side) would be reached at 10 feet, at which
height accordingly the width would be reduced to the postulated
standard of 6 feet.3
These considerations are hypothetical,-and we base only one
positive statement upon them, viz., that the hitherto received
estimate of 20 feet as the height is impossible.4 This, however,
was only a guess, based on no ancient authority.
As regards the shape and character of any battlement crowning
the vallum, any direct conclusion would be guesswork. Possibly
1 Philips, Article 199. "The retaining slope is only f, as sods are not strong
enough to support earth at J."
2 The apparent average slope actually yielded by the sections was not so high
as this, being 2 upon 1 at Croy No. 11, and about upon 1 at Croy No. 12a.
But compare the facts at Barr Hill No. 1.
3 Obviously, if the breadth was greater than 6 feet (say, 8 feet), the probable
height must fall correspondingly.
4 It is curious to note that one of the sixteenth century Scottish historians—
the moat imaginative of them all, Hector Boeee—hit on very nearly the correct
dimensions of the base when he said that the wall was 8 cubits broad [between
12 and 15 feet] and 12 cubits high (Boece's Scotorum Historiae, lib. vii., ed. 1574,
p. 1246). According to Bede (by far the best evidence), the height of the North
English mums in his time was 12 feet.