One of (many) wonderful things about Northumberland is the incidence of extremely ancient and mysterious rock carvings
http://rockart.ncl.ac.uk/ - which I invite interested readers to browse.
These carvings have the power to create a powerful feeling of connection with people of the past - and irresistibly lead to speculations about what these markings are for?
I have my own theory, naturally!, which is that they are symbolic maps - used for teaching about significant landscape features.
For instance, the concentric rings like those shown in the above illustration are representing 'hill forts' - such as this one at Lordenshaws (aerial photo):
and the carved lines represent either paths or rivers.
Since many of these landscape features will be undiscovered, lost or altered; and since I would not expect a symbolic map to resemble closely the actual landscape - my theory has the virtue of being both psychologically gratifying and essentially un-disproveable!