Surveys by the writer in Britain and Germany have recently revealed a consistent pattern of Roman frontier communications in which each system's minor installations were sited so as to be able to see, and thus to signal to, their nearest fort, whilst the forts themselves could be linked to form a unified chain. But, until recently, the Antonine Wall appeared so different that it seemed unlikely that it operated in the same way. Comparing the two British Walls, both share the basic framework of a rampart and ditch and the change from stone to turf construction, on the northern system, is mere detail, but differences in the garrison installations did seem to have been of operational importance. For example, the inter-fort spacings of the Antonine Wall were much shorter, varying from 1.56 to 3 Roman miles, as against 6 to 9 on Hadrian's Wall – producing 17 known (including Carriden) and several suspected forts in c. 40½ Roman miles, as opposed to 16 in 80 Roman miles on the southern Wall. Moreover, many Antonine Wall forts were too small to have held a full auxiliary unit and there seemed to be no sign of a fortlet and turret system.