Sorry, but I don't know who posted this quote.....
"Of the many purposes of Silbury, I believe it was also incorporated to be part of a "line of sight", message relay network, from the Southern/Western coasts of the UK towards the London area, as was done on the Great Wall of China, to alert central authorities of any invasions."
....but so far as we know, when Silbury was built there were no "central authorities" in the modern sense, no organised "invasions" (lots of cross Channel trade) and the site of London was a few small hills and islands beside a wide and boggy river.
Jim.