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Is Silbury an only child?

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robvxvx R
robvxvx Sep 26, 2008 20:14:09
Replying to robvxvx

Whilst Stoneshifter's theory on the origin of the shape of Silbury type mounds is certainly interesting (and I'm not saying it's wrong....it could be correct) , it is also a large intuitive leap (and hey there's been many a mystery solved in that fashion), I propose that there is a much simpler explanation.

All ancient civilizations (pre-concrete) had a similar problem if they wanted to build a tall structure, they had to make it's base at least as broad as it's height [e.g. Pyramids(cental and south american, egyptian and chinese), ziggurats, prehistoric mounds and indeed Saxon and Norman motte structures].

All had to slope inwards by necessity, and as examples of egyptian pyramids for example will show only a certain steepness of angle can be
achieved before the sides slump and collapse. therefore by trial and error most cultures found the maximum achievable angle(for the given building material) was....and most would have opted for something approaching the maximum because this would reduce base area and thus amount of material required.

The reason for round shaped monuments I'm sure is because if you're building in softer medium - i.e. not brick or stone - corners are unstable (and before anybody points out the amerindians of the mississipian culture built square earth mounds - which I'm sure someone would...lol - They built relatively low squat mounds(max height did not appear to be their aim) and even They had to give the corners very gentle radii) and the round shape gives the greatest stability.

Which brings us back to the problem of why it's so hard without excavation to be sure of the origin of so many mounds (in the British isles at least) the Ancient mound builders and the Saxon/Norman builders faced the same engineering issues in building their mounds if not the same reasons for building them. And by necessity they built in very similar ways, which ironically made it so easy for the ancient mound to be re-used by the medieval castle builders(who I'm sure assumed that the mounds-in the case of the larger ones, had been built originally for the same purpose).

but basically I believe the choice of shape was an almost purely pragmatic one.

N nigelswift
nigelswift Sep 26, 2008 21:07:24
Replying to robvxvx

"only a certain steepness of angle can be achieved before the sides slump and collapse. therefore by trial and error most cultures found the maximum achievable angle(for the given building material) was....and most would have opted for something approaching the maximum because this would reduce base area and thus amount of material required."

I think that's right. EH's consultant engineer said Silbury's slope was at, not beyond, the optimum before soil-slip would happen. Silbaby has an identical slope.

It's reasonable to suspect that's the slope they would have aimed at since it's the most efficient in terms of amount of material versus height, as you say.
OR that in some cases they overdid it, in which case erosion would happen and the slope would reduce to the optimum one over time.

Soil slip is only a factor with soil and loose material of course. Is this a reason to believe that covering it with soil or loose chalk was in the job specs for Silbury from the start? Probably - and the turf which then developed is arguably the one feature that has ensured the main structure and profile of Silbury has remained unaffected and unaltered for millenia, IMO. Did they know this as well? I reckon so and that they were a bit damn clever.