Once the supply system had been designed, Septimius Severus's command planned a mass advance north along Dere Street in AD 209. The account interprets the replacement of a fort's buildings with ordered rows of roundhouses as a concentration camp for refugees fleeing the devastation farther north. That use of the site remains an interpretation of its archaeological remains. The army would later divide, with Caracalla taking two-thirds along the Highland Boundary Fault and building forts to block the glens. The Classis Britannica would close the eastern coast, restricting the local population's routes of escape. Severus would lead the remaining third across the Forth and through Fife into the upper Midland Valley. Poor weather delayed the start, but restless troops helped force the decision to advance. Marching camps approaching 70 hectares housed the combined force, and their crop marks help trace its route. The Antonine Wall was also repaired and manned to protect the army's rear as it moved north.
Chapter · 45:31-48:47
The operational design of Severus's Scottish campaign
The Roman plan combined a mass advance up Dere Street, a later division of the army, and naval closure of the eastern coast to isolate the communities in its path.