Caracalla took the larger, two-thirds portion of the Roman army across the Forth. In Simon Elliott's reconstruction, the legionary spearhead probably comprised the three legions based in Britain, supported by British auxiliaries familiar with the theatre. The force advanced northeast along the Highland Boundary Fault and built a sequence of marching camps of about 54 hectares. Those camps provided the basis for forts intended to block the glens once the advance reached the coast. Crop marks and archaeological remains help reconstruct the route and the physical scale of this part of the campaign.
Notable Point · 51:05-52:05
Caracalla's advance and the 54-hectare marching camps
The size and alignment of Caracalla's camps connect the divided Roman army with the later system of glen-blocking forts.