At some point towards the end of the first century, the Romans withdrew the majority of their forces from Scotland to the territory of the Brigantes, who controlled Northern England. Their main base was set up at York and occupied by the twentieth legion. The Brigantes had long been loyal to Rome and provided a key buffer state for the Lands to the south. We also presume that some political relations continued with former allies in Scotland, although everything between the campaigns of Agricola and the building of the wall 40 years later is very sketchy.
At this point Hadrian arrives, possibly in response to a revolt in the north involving the Brigantes, who may have been triggered by the death of Trajan. Hadrian brought fresh troops, and re-established a ‘frontier’ in the North of Brigantes territory. After 80 years, the Romans understood that most of what they valued was in the South, so the north was no more than a security zone.