[336] For this wall see the admirable account by Dr. George Macdonald, The Roman Wall in Scotland, Glasgow, 1911.
[337] The best description of the internal arrangements of a mile-castle is given by Mr. F. G. Simpson, in the Transactions of the Cumberland and Westmoreland Archaeological Society, vol. xi, New Series.
[338] The German Limes-Commission has not yet published its report on these works and the course of the frontier line in general. On the Walldürn-Welzheim section, which was built by Pius, the towers are at intervals of from 250 to 400 metres. Pelham, op. cit., p. 204.
[339] The view with which I find myself in most agreement is that of Delbrück, Geschichte der Kriegskunst, ii. 155-60.
[340] See Pelham, op. cit., p. 201 and appendix.
[341] The torches which project from the upper stories of the block-houses represented on the Trajan column have often been noted as indicating some method of fire-signalling.
[342] The palisade was not, of course, a board fence which could be torn down in a few minutes. It was made of oak-trees split in halves and bedded in a ditch four and a half feet deep. See Pelham, op. cit., p. 200. Some idea of its appearance can be gathered from the representation at the beginning of the reliefs on the Marcus column.
[343] Oman, Art of War in the Middle Ages, p. 209. He quotes Nicephorus Περὶ παραδρομῆς πολέμου.
[344] The stone wall on the Raetian frontier is of very inferior construction.
[345] The garrisons were: at Netherby, the Cohors I Aelia Hispanorum M. E., vii. 954, 963, 964, 965; at Bremenium, the Cohors I Fida Vardullorum M. E. and exploratores, vii. 1030, 1043; at Habitancium, the Cohors I Vangionum M. E., exploratores and Raeti Gaesati 1002, 1003. The latest inscription at Netherby dates from the reign of Severus Alexander; at Bremenium, the most advanced of the Dere Street forts, from the reign of Gordian III.