COMPARISON OF VAREOUS DEFENSIVE STRUCTURES. 



105 



sometimes, if the camps were of large size, there were several passages upon each 

 side. These entrances were usually protected by exterior mounds, or by overlap- 

 ping walls, and occasionally outworks were erected. The temporary camps, castra 

 cBstiva, or those not designed for constant occupation, had comparatively slight 

 entrenchments, the ditch being about six feet deep, and the parapet behind it only 

 about four feet high. The castra stativa were generally much smaller than the 

 temporary camps, and were strongly protected. They were designed to contain 

 garrisons, either to guard a frontier or keep in awe newly conquered provinces. 

 Two ranges of them were erected shortly after the time of Agricola, upon the 

 frontiers of Caledonia, placed at short intervals apart between the Clyde and Forth, 

 and the Tyne and Solway, nearly upon the line afterwards occupied by the walls of 

 Hadrian, Antoninus Pius, and Severus. The smaller sort of castra stativa were 

 termed castella, answering in a great degree to the field-forts and redoubts made 

 use of by modern armies. 



The above cut, Fig. 35, is a plan of the camp of a single Roman legion, according 

 to Polybius, and is introduced more to illustrate the different methods of protecting 

 the gateways, than to serve any other purpose. In some of the Western military 

 works, as may be seen by reference to the first volume of these Contributions, 

 gateways occur similar to that at A. In the more regular structures of the West, 

 however, the mound covering the gateway is invariably placed interior to the walls, 

 which circumstance, joined to others less equivocal, goes to sustain the conclusion 

 that such works were not constructed for defence. The Roman camps had fre- 

 quently two, sometimes four or more, lines of embankment, with flanking defences, 

 horn-works, etc. The stone and earth circles of England are all ascribed to the 

 Celts ; the rectangular works to the Romans. Throughout the islands, no works 

 occur in which the two figures are combined, as in the Mississippi valley. 



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