And Antonine wall higher up to keep the worst of them further from civilisation. The Highlanders!!!!
Seriously, the Highlanders were heathens from a much later period but it shows how the lowlands Scot and those from higher north have long been treated differently. Hadrian's wall was a money making customs wall. You can trade nicely, and more importantly scalp them, with the lowland Scot. Less so the further north which iirc was more defensive than business in function.
The above may be tongue in cheek or not. But there are civilised people north of the lowlands. Afterall there's been talk in the far north of SCEXIT!!! That's civilisation!!!