"as the Romans had a habit of intentionally running their routes past existing megalithic sites "

Didn't they though! At Belsay in Northumberland, a road goes in between a burial mound (The Poind) and it's stone (The Man).
http://www.themodernantiquarian.com/site/3340
It makes me tetchy to think about it, 'cos there's also a certain bloody great wall that runs roughshod over a whole load of lovely bits and pieces not far away.

Hmpf! Bloody wall.... Tut.

<Wanders off to mumble to himself in a corner>