I think it may be more mysterious than Stonehenge and Avebury, really, in the sense that they, although not entirely fathomable by any means, nevertheless yield certain information – the alignments give one at least some sense of their significance and purpose. Silbury is silent. As far as I recall (and I should really read up *before* writing this, but I will do it shortly…), we have almost nothing on Silbury: no significant burials, and of course it’s hard to align a mound with anything in particular.
I was reminded passing it yesterday that it is actually notably recessed: although its crown is visible for some way (a Roman road nicely traverses a field towards it and then deflects), which is curious. But it seems too small – and too much effort to construct – for a defensive structure, and again perhaps too much effort for a purely ceremonial one. Though what else it could be I don’t know. It’s beautiful.