Roman Road is to the North of Salisbury – it connects Devizes Road to the Wilton Road.
I think it is part, or possibly a continuation, of The Portway, which is the Roman road which connected Dorchester to London.
I have drawn what I’m guessing is the old route of the Roman Road on Google Maps, but this may not be accurate – the maps that I’ve found don’t got down to this level of detail. Also, although you can clearly see a straight line of trees on Google maps, which continues the straight line of Roman Road, I do not know if this is a currently existing path. It could be the path known as ‘Broken Bridges’, but, from memory, I wouldn’t think that the path quite lines up with Roman Road.