glasgow archaeological society.
they either crush to pieces or break down." A last quotation
from this author shows that the war regulations of his day
justified his high view of the functions of these engines, not
merely for the defence of a city, but as a wing of an army on
march. For every 100 men in a legion there was one carrobalista,
each requiring eleven men to manage it. These were powerful
crossbows mounted on moveable carriages drawn by pairs of
horses or mules. They threw darts or arrows for a long distance
and with great force.1 These carrobalista} are represented on
the Trajan column. They were used both in camps and
in the open field. The equipment of a legion required ten
engines of the onager type, one onager for every cohort. Like
the carrobalista they were transportable, and could be mounted
on carriages drawn by two oxen. " Thus," concludes Vegetius,2
" if the enemy shall happen to come to attack the vallum, the
camp may be defended with arrows and with stones."
The purpose of these numerous citations is to suggest the
a priori probability that methods of defence employed in
Roman camps might apply to the defence of a trans-isthmian
vallum. It needs no proving that the rampart of Antonine was
guarded by the soldiers with the usual personal arms. The
finding of occasional stone projectiles along the line of the wall
suggests that the system of defence included artillery.3
8. The Periodic Expansions on the South Face
of the Wall.
The expansions occurring at the Croy Hill sections Nos. 11
and 12a are not exceptional, but are simply examples of a
phenomenon repeated at intervals all along the vallum wherever
it is preserved. The expansions at these sections are the only ones
of which through sections have yet been made. A reference to the
descriptions of them will show the particular details for the follow-
1 Vegetius, ii. 25 ; iii. 24.
2 Vegetius, ii. 25. " Item decern onagri hoc est singuli per singulas cohortes in
carpentis bubus portantur armati ut si forte hostes ad adpugnandum venerint
vallum sagittis et saxis possint castra defend!."
' 3 This matter is further discussed in the next section.