CHAPTER II
The Fort and its Defences
Various Occupations
AT a comparatively early stage in the investigation of the fort, it became clear that there were at least two occupations to be reckoned with, and that the fort whose defences were first encountered had been partly built above another fort which was smaller in size, and therefore earlier in date. The evidence regarding the successive periods of occupation will be discussed in detail later. In the meantime it is sufficient to point out that we have really to deal with two forts, somewhat different in outline,—an early fort that probably witnessed only a single period of occupation, and a somewhat larger fort which bears unmistakable marks of having undergone considerable change and alteration from time to time while it was still in Roman hands. Among the forts already excavated in Scotland, Birrens, Camelon, Rough Castle, and Ardoch, as well as possibly others, have yielded evidence that is suggestive of more than one occupation. The plan of Bar Hill alone shows two distinct systems of fortification. One feature which the early forts at Newstead and Bar Hill have in common is a certain irregularity in the plan of their defences. This at once distinguishes them from the type of castellum so common on the German Limes, with its long straight ditches following the line of the walls, and its gates with flanking towers. The difference is typical of the change from earthen ramparts to walls of stone. Many of the devices employed by the earlier engineers must have been rendered unnecessary when stone walls with battlements took the place of mere mounds of earth. And so it is that continental parallels to the original castella at Newstead and at Bar Hill must be sought in works which are older than the close of the first century of our era. The ditches that guarded the Agricolan fort at Bar Hill recall those that protected the
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