nigelswift wrote:
Well you can see Silbury from the Sanctuary obviously so vice versa too, and you can see both from the top of Silbaby (in the case of the Sanctuary, if you peer through the Silbaby trees) and the two are almost exactly 180 degrees apart (see Ocifants diagram http://www.themodernantiquarian.com/site/6766/silbaby.html )
Using Google street it seems Silbury can't be seen from Nash road by the Longstones due to the rise in the ground between.I've also walked along a lot of the river when dry and can't recall Silbury being hidden.
https://maps.google.co.uk/maps?q=avebury&hl=en&ll=51.422126,-1.872424&spn=0.007065,0.021136&sll=53.395717,-1.499456&sspn=0.216183,0.676346&t=h&hq=avebury&z=16&layer=c&cbll=51.422126,-1.872424&panoid=XMK0ibjAdfLXowNG0iyzhQ&cbp=12,82.81,,0,7.95