Maen Llia 7
Image by cerrig

nigelswift wrote:
"useless in practice , unless you ignore the bogs , rivers , lochs and contours"

I don't know, it IS useful to have some prominently visible features at both your origin and destination, they give you a nice sense of the straight line between the two and then you make pragmatic diversions as and when you encounter bogs and rivers etc. I used to navigate in London that way, trying to keep the sun at a particular angle to my car for as much of the journey as possible. It works well and you can choose dozens of routes and go for miles and still get there or thereabouts efficiently. So I think Alfred was probably onto something but I agree, you could never demonstrate it on a map only on the ground - by seeing whether the points were prominently visible. So the 2 cases are rather similar.

But he connected churches of any date (you just never know how often they are the site of something much older etc gets trotted out to justify the choice ),Iron Age " hill forts " ,moats , ponds , prehistoric sites , natural features .
People tend to know their environment and those tht manage to get around the world over don't seem to use his method .Outwith woodland and on the sea/oceans the sun and stars are useful elsewhere natural features can help ,but man made features are only useful in retrospect not built for that purpose .

A couple of observations:

Maybe worth mentioning that many monuments that are "clearly" related (at least in terms of date/type/proximity) aren't necessarily all visible from each other, though some might be visible from some of the others. Some of the South Wales monuments may be not visible from each other due to a rise in the intervening ground. Postie and I saw good examples of this at Y Pigwyn, a few miles NW of the Maen Llia monuments.

Conversely those same monuments might all be visible from a different (often higher) vantage point. The summit ridge or western slopes of Fan Llia may be the "best" place to see the Maen Llia monuments from collectively, for example.

I would also chuck in that contemporaneity isn't always essential for monuments to be "related" either. Plenty of long barrows have round barrows built close by that evidently have a relationship with the much earlier monument (even if we don't know what that relationship is, exactly).

Even with good 5m contours, a 1/25000 map doesn't show you the folds in the land all that accurately. Here's a site that looks straight from above/on the map, but appears to curve on site:
http://www.themodernantiquarian.com/post/89397/down_tor.html

In any case, a surveyor won't lay a tape between two points on a slope and then use that measurement alone as the basis of the length of line he draws on his 2D map. A line measured from his 2D map will be shorter than the length measured on the ground, as he would need to correct for the slope. http://en.wikipedia.org/wiki/Tape_correction_(surveying)#Correction_due_to_slope

Can't say I've considered equidistance at sites before, personally. Something new to think about!

I would tend to agree (based on nothing more scientific than visiting sites without measuring anything at all) that topography plays a bigger part than equidistance in placement of monuments in proximity.

Yes I appreciate a lot of his monuments were from different eras, I guess what I was meaning was whether anyone built them or not they can be useful to have them in your head. But then again, maybe that's a fancy way of saying if you want to go to Glastonbury Tor, head towards it, which is definitely a method they used in the old days ....