[326] e.g. Friedberg has an area of (roughly) 10 acres, Okarben of 14, Heddernheim of 13, and Kesselstadt of 35. A cohort of 500 infantry was usually allowed about 5 acres. [327] See Macdonald, _The Roman forts at Barr Hill_, pp. 11-15; Curle, _A Roman Frontier-post_, pp. 29, 349. [328] xi. 6344 ‘P. Cornelio P. f. Sab(atina) Cicatriculae prim(o) pil(o) bis, praefect(o) equit(um), praef(ecto) clas(sis), praef(ecto) cohortium quattuor civium Romanor(um) in Hispania, trib(uno) mil(itum)’. [329] iii. 14147². [330] _W. D. Z._ xxi. 186, where this theory of the first-century frontier system is further developed. [331] See Pelham, _op. cit._, p. 199. The forts on the North British frontier range in area from 2½ to 5½ acres, the largest (Amboglanna) being designed to hold a _cohors miliaria peditata_. The German forts seem to have been on a rather larger scale, and ran up to 15 acres, which is the area allowed at Aalen to an _ala miliaria_. It is not meant, of course, that forts of this type did not exist in the first century, but it was not until the reign of Hadrian that the dispersion of the auxilia in separate units was adopted as a general policy. [332] Cf. iii. 3385 ‘(Commodus) ripam omnem burgis a solo extructis item praesidis per loca opportuna ad clandestinos latrunculorum transitus oppositis munivit’. This is from the Danube frontier. [333] _Historia Augusta, Vita Hadriani_, 12 ‘In plurimis locis in quibus barbari non fluminibus sed limitibus dividuntur, stipitibus magnis in modum muralis saepis funditus iactis atque conexis barbaros separavit’. [334] The best recent account of this frontier in English is Pelham’s essay, ‘The Roman Frontier in Germany,’ in the work already cited. [335] Recent researches have, however, made it very doubtful whether a turf wall ever preceded the stone wall along the whole line. [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.